Coated polymer particles comprising a water-swellable polymer core and a sol-gel coating

Abstract

The present invention relates to coated polymer particles comprising a water-swellable polymer core and an essentially continuous coating encapsulating the core. The coating comprises an oxide, hydroxide or oxide hydrate of silicon, aluminum, zirconium, tin or titanium. The polymer particles do not show instantaneous swelling, when contacted with water or a water-containing liquid, but show delayed water absorption after an appropriate period of time. The coated polymer particles may be used in oil fields, in mining, for construction chemical compositions or as carrier for active substances. The coated polymer particles are prepared by a suspension coating process or a fluidized bed coating process.

Claims

1. Coated polymer particles comprising (a) a water-swellable polymer core comprising a copolymer comprising sulfo group- and/or quaternary ammonium group-comprising structural units; and (b) an essentially continuous coating encapsulating the water-swellable polymer core, the essentially continuous coating comprising an oxide, hydroxide or oxide hydrate of silicon, aluminum, zirconium, tin, titanium or a mixture thereof, wherein a mass ratio of the oxide, hydroxide or oxide hydrate to the water-swellable polymer core is from 0.002 to less than 1.

2. The coated polymer particles of claim 1, wherein the water-swellable polymer core comprises a copolymer P1 and/or a copolymer P2, wherein the copolymer P1 comprises sulfo group- and amide group-comprising structural units, and the copolymer P2 comprises quaternary ammonium group- and amide group-comprising structural units.

3. The coated polymer particles of claim 2, wherein the copolymer P1 comprises (i) sulfonic acid-comprising structural units of formula (I) ##STR00005## wherein R.sup.1 represents hydrogen or methyl, R.sup.2, R.sup.3 and R.sup.4 each independently represent hydrogen, a C.sub.1-C.sub.6-alkyl group or a C.sub.6-C.sub.14-aryl group, M represents hydrogen, a metal cation or an ammonium cation, wherein the metal cation has a valency V, and a represents 1 or 1/V, (ii) (meth)acrylamido-containing structural units of formula (II) ##STR00006## wherein R.sup.1 represents hydrogen or methyl, and R.sup.5 and R.sup.6 each independently represent hydrogen, a C.sub.1-C.sub.20-alkyl group, a C.sub.5-C.sub.8-cycloalkyl group or a C.sub.6-C.sub.14-aryl group, (iii) structural units derived from monomers having two or more ethylenically unsaturated vinyl groups, and (iv) optional structural units derived from monomers having one ethylenically unsaturated vinyl group, wherein the optional structural units are different from the structural units of (i) and (ii), and wherein the copolymer P2 comprises (i) cationic structural units of formula (III) ##STR00007## wherein R.sup.1 represents hydrogen or methyl, R.sup.7, R.sup.8, R.sup.9 and R.sup.10 each independently represent hydrogen, a C.sub.1-C.sub.20alkyl group, a C.sub.5-C.sub.8-cycloalkyl group or a C.sub.6-C.sub.14-aryl group, m represents an integer of 1 to 6, X represents oxygen or an N—R.sup.10 group, Y.sup.−arepresents halogen, a C.sub.1-C.sub.4-alkylsulfate group, a C.sub.1-C.sub.4-alkylsulfonate group or sulfate, and a represents ½ or 1, (ii) (meth)acrylamido-containing structural units of formula (II) ##STR00008## wherein R.sup.1 represents hydrogen or methyl, and R.sup.5 and R.sup.6 each independently represent hydrogen, a C.sub.1-C.sub.6-alkyl group or a C.sub.6-C.sub.14-aryl group, (iii) structural units derived from monomers having two or more ethylenically unsaturated vinyl groups, and (iv) optional structural units derived from monomers having one ethylenically unsaturated vinyl group, wherein the optional structural units are different from the structural units of (i) and (ii).

4. The coated polymer particles of claim 3, wherein the copolymer P1 comprises (i) 10 to 70 mol-% of structural units of formula (I), (ii) 29.99 to 89.99 mol-% of structural units of formula (II), (iii) 0.01 to 1 mol-% of structural units derived from monomers having two or more ethylenically unsaturated vinyl groups, and (iv) 0 to 30 mol-% of structural units derived from monomers having one ethylenically unsaturated vinyl group, wherein the mol-% of (i), (ii), (iii) and (iv) add up to 100 mol-%, and the copolymer P2 comprises (i) 10 to 70 mol-% of structural units of formula (III), (ii) 29.99 to 89.99 mol-% of structural units of formula (II), (iii) 0.01 to 1 mol-% of structural units derived from monomers having two or more ethylenically unsaturated vinyl groups, and (iv) 0 to 30 mol-% of structural units derived from monomers having one ethylenically unsaturated vinyl group, wherein the mol-% of (i), (ii), (iii) and (iv) add up to 100 mol-%.

5. The coated polymer particles of claim 2, wherein the water-swellable polymer core comprises a mixture of the copolymers P1 and P2 in a molar ratio of 99/1 to 85/15.

6. The coated polymer particles of claim 1, wherein a number average diameter of the coated polymer particles is in a range of 10 to 1000 μm.

7. The coated polymer particles of claim 1, wherein an average layer thickness of the essentially continuous coating is in a range of 100 to 1000 nm.

8. The coated polymer particles of claim 1, wherein the coated polymer particles have an average sphericity (mSPHT) of at least 0.90.

9. The coated polymer particles of claim 1, wherein the essentially continuous coating comprises an oxide or oxide hydrate of silicon, aluminum, zirconium, tin, titanium or a mixture thereof.

10. The coated polymer particles of claim 9, wherein the essentially continuous coating comprises an oxide of silicon, aluminum, zirconium or a mixture thereof.

11. The coated polymer particles of claim 1, wherein the coated polymer particles comprise an active substance.

12. The coated polymer particles of claim 2, wherein the water-swellable polymer core comprises a mixture of the copolymers P1 and P2 in a molar ratio of 1/99 to 15/85.

13. The coated polymer particles of claim 1, wherein the essentially continuous coating is grown on the water-swellable polymer cores via polycondensation of a condensable precursor or a hydrolysable and condensable precursor.

14. A process for preparing the coated polymer particles of claim 1, the process comprising (a) suspending water-swellable polymer core particles in an organic solvent to obtain a suspension, (b) adding a precursor of an oxide, hydroxide or oxide hydrate of silicon, aluminum, zirconium, tin, titanium or a mixture thereof to the suspension, wherein the precursor collocates at a particle solvent interphase boundary, (c) convening the precursor to an oxide, hydroxide or oxide hydrate of silicon, aluminum, zirconium, tin, titanium or a mixture, and (d) obtaining a water-swellable polymer core coated with an essentially continuous coating encapsulating the water-swellable polymer core, wherein (b) and (c) are optionally repeated once, twice or three to ten times.

15. The process of claim 14, wherein the organic solvent is selected from the group consisting of a C.sub.1-C.sub.12-alcohol, an aromatic hydrocarbon, an aliphatic hydrocarbon and a mixture thereof, wherein the C.sub.1-C.sub.12-alcohol has one, two or more than two hydroxy groups.

16. A process for preparing the coated polymer particles of claim 1, the process comprising (a) fluidizing water-swellable polymer core particles in a stream of a fluidizing gas, (b) contacting the water-swellable polymer core particles with a solution or dispersion of a precursor of an oxide, hydroxide or oxide hydrate of silicon, aluminum, zirconium, tin, titanium or a mixture thereof, to coat the water-swellable polymer core particles with the precursor, (c) converting the precursor to an oxide, hydroxide or oxide hydrate of silicon, aluminum, zirconium, tin, titanium or a mixture thereof to obtain coated particles, and (d) drying the coated particles.

17. The process of claim 14, wherein the precursor is selected from (a) a tetra-C.sub.1-C.sub.4-alkoxysilane, a tri-C.sub.1-C.sub.4-alkoxy-C.sub.1-C.sub.4-alkylsilane, a tri-phenyloxy-C.sub.1-C.sub.4-alkylsilane, a tri-C.sub.1-C.sub.4-alkoxy-phenyl-silane, a di-C.sub.1-C.sub.4-alkoxydi-C.sub.1-C.sub.4-alkylsilane, a di-phenyl-phenyloxy-C.sub.1-C.sub.4-alkylsilane, a di-C.sub.1-C.sub.4-alkoxydi-phenyl-silane, a vinyltri-C.sub.1-C.sub.4-alkoxysilane, a vinyltriphenyloxysilane, a (meth)acryloxy-C.sub.1-C.sub.4-alkoxytri-C.sub.1-C.sub.4-alkylsilane, a (meth)acryloxy-C.sub.1-C.sub.4-alkyltri-C.sub.1-C.sub.4-alkylsilane, a (meth)acryloxy-C.sub.1-C.sub.4-alkyldi-C.sub.1-C.sub.4-alkyl-C.sub.1-C.sub.4-alkoxysilane, a (meth)acryloxy-C.sub.1-C.sub.4-alkyl-C.sub.1-C.sub.4-alkyl-C.sub.1-C.sub.4-dialkoxysilane, a (meth)acryloxy-C.sub.1-C.sub.4-alkyltri-C.sub.1-C.sub.4-alkoxysilane, and a partially pre-reacted or pre-hydrolyzed product thereof; a halide, a C.sub.1-C.sub.4-alkoxide, a carboxylate of aluminum, zirconium, tin or titanium; and a partially pre-reacted or pre-hydrolyzed product thereof; (b) an alkali metal silicate or metasilicate; and a partially pre-reacted or pre-hydrolyzed product thereof; and (c) a mixture thereof.

18. The process of claim 14, wherein (c) comprises: (i) hydrolyzing and/or acidifying the precursor to obtain an activated precursor, and (ii) subjecting the activated precursor to a polycondensation reaction.

19. A chemical composition suitable for an oil field application, a mining application or a construction application, wherein the chemical composition comprises the coated polymer particles of claim 1.

Description

(1) The following figures and examples are intended to illustrate the invention in greater detail.

(2) FIG. 1 shows two electron microscopy pictures of coated polymer particles according to the invention, obtained by a suspension coating process. The picture on top shows coated particles as a whole, the picture at the bottom shows a cross-section through said particles and illustrates the continuous coating of the polymer core.

(3) FIG. 2 shows an electron microscopy picture of the coated polymer particles of example 8.

(4) FIG. 3 shows an electron microscopy picture of the coated polymer particles of example 9.

EXAMPLE 1

(5) Copolymer 1 (Anionic Superabsorbent Copolymer)

(6) A 2 L double jacketed reactor was charged with 600 g of white spirit D40 (available from Miller Chemie, Germany). After addition of 3 g Span® 80 (sorbitane monooleate, available from Sigma Aldrich, Germany) and a stabilizer (copolymer of alkyl acrylates or methacrylates with acrylic and methacrylic acid) the reactor was purged with nitrogen for 90 min, while the mixture was stirred at a rotation speed of 300 rpm. The monomeric phase was prepared in a separate vessel: Said vessel was charged with water (7.2 g) and 160.81 g (21.97 mol-%) of the sodium salt of 2-acrylamido-2-methylpropanesulfonic acid (50 wt.-% solution in water), 161.29 g (70.99 mol-%) acrylamide (50 wt.-% solution in water), 8.11 g (7.01 mol-%) acrylic acid (99.5 wt.-% concentrated solution) and 4.04 g (0.03 mol-%) methylenebisacrylamide (2.0 wt.-% concentrated solution) were added successively and neutralized with 7.93 g of a 50% sodium hydroxide solution, in order to adjust the pH to a value of 6.0. Additionally 3.60 g of an aqueous 4% V50 solution (2,2′-azobis(2-amidinopropane)dihydrochloride; WAKO Chemicals) and 3.60 g of an aqueous 1% sodium bisulfite solution were added to the aqueous phase. Said aqueous phase was added to the oil phase in the reactor and the oil-water-mixture was dispersed for 2 min at a rotation speed of 300 rpm. The polymerization was initiated by addition of 3.6 g of an aqueous 0.5% solution of tert-butylhydroperoxide. The reaction mixture was stirred for 30 min. Thereafter, water was distilled off azeotropically (620 rpm, 50 mPa, 60° C.). The resulting polymer beads were filtered, washed with acetone and dried at 40° C. for 6 h in a drying chamber.

EXAMPLE 2

(7) Copolymer 2 (Anionic Superabsorbent Copolymer)

(8) Oil phase and aqueous phase were prepared in separate beaker glasses. For the preparation of the oil phase 10.7 g Span® 80 (available from available from Sigma Aldrich, Germany), 35.6 g of a stabilizer (copolymer of alkyl acrylates or methacrylates with acrylic and methacrylic acid) and 295 g white spirit D40 (aliphatic hydrocarbon mixture, available from Miller Chemie, Germany) were mixed. For the preparation of the aqueous phase 191.04 g (22.01 mol-%) of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid (50 wt.-% solution in water), 191.18 g (70.94 mol-%) acrylamide (50 wt.-% solution in water), 0.2 g Trilon® C (50% solution of diethylentriaminepenta-acetic acid, pentasodium salt, available from BASF SE, Germany), 4.79 g (0.03 mol-%) methylenebisacrylamide (2.0 wt.-% concentrated solution) and 9.63 g (7.02 mol-%) acrylic acid (99.5 wt.-% concentrated solution) were mixed and neutralized with 23.84 g of a 20% sodium hydroxide solution, in order to adjust the pH to a value of 6.0. Afterwards, 5.6 g of water were added to the aqueous phase. Oil phase and aqueous phase were then mixed in one beaker glass and homogenized for 1 min at 10000 rpm. A 2 L double jacketed reactor was then charged with the resulting mixture and adjusted to 15° C. During the adjustment of the temperature the reactor was purged with nitrogen at 300 rpm. The polymerization reaction was initiated by dropwise addition of 0.16 g of an aqueous 0.5% solution of tert-butylhydroperoxide and an aqueous 0.16 g 1.0% solution of SO.sub.2. Said addition was controlled in a way that the temperature increase was not exceeding 1° C./min until a maximum reaction temperature of 40° C. The amount of unreacted acrylamide was lowered by addition of azo-bis-(isobutyronitrile) (24 g of 4 wt.-% methanolic solution) at 80° C. and stirring. Thereafter, water was distilled off azeotropically.

EXAMPLE 3

(9) In Situ Coating

(10) A 2 L double jacketed reactor was charged with 600 g of white spirit D40 (available from Möller Chemie, Germany). After addition of Span® 80 (3 g, available from available from Sigma Aldrich, Germany) and a stabilizer (copolymer of alkyl acrylates or methacrylates with acrylic and methacrylic acid) the reactor was purged with nitrogen for 90 min, while the mixture was stirred at a rotation speed of 300 rpm. The monomeric phase was prepared in a separate vessel: Said vessel was charged with water (7.2 g) and 160.81 g (21.97 mol-%) of the sodium salt of 2-acrylamido-2-methylpropanesulfonic acid (50 wt.-% solution in water), 161.29 g (70.99 mol-%) acrylamide (50 wt.-% solution in water), 8.11 g (7.01 mol-%) acrylic acid (99.5 wt.-% concentrated solution) and 4.04 g (0.03 mol-%) methylenebisacrylamide (2.0 wt.-% concentrated solution) were added successively and neutralized with 7.93 g of a 50% sodium hydroxide solution, in order to adjust the pH to a value of 6.0. Additionally, 3.60 g of an aqueous 4% V50 solution (2,2′-azobis(2-amidinopropane)dihydrochloride; WAKO Chemicals) and 3.60 g of an aqueous 1% sodium bisulfite solution were added to the aqueous phase. Said aqueous phase was added to the oil phase in the reactor and the oil-water-mixture was dispersed for 2 min at a rotation speed of 300 rpm. The polymerization was initiated by addition of 3.6 g of an aqueous 0.5% solution of tert-butylhydroperoxide. The reaction mixture was stirred for 30 min. Thereafter, water was distilled off azeotropically (620 rpm, 50 mPa, 60° C.).

(11) Thereafter, 0.85 g of neopentylglycol were added at 20° C. Then SiCl.sub.4 (17 mL) was injected and the mixture was stirred at 300 rpm for 12 h. The resulting coated polymer beads were filtered, washed with acetone and dried at 40° C. for 6 h in a drying chamber.

EXAMPLE 4

(12) 2-Step Coating

(13) Polymer beads as obtained in Example 1 (5 g) were re-dispersed in a 250 mL three-neck flask by addition of 1.25 g Triton®-X-100 (available from Dow Chemical Company, USA) and 150 mL ethanol. Under slight stirring aluminum isopropoxide (1.25 g) and tetraethoxysilane (0.5 mL) were added. After 12 h of stirring the supernatant was removed and the thus obtained coated polymer beads were washed with ethanol and transferred into a vessel charged with 50 mL of toluene. Then SiCl.sub.4 (5 mL) was added. After 5 h of stirring (60° C.) the resulting polymer beads with a double coating were washed with hexane and dried at 30° C.

EXAMPLE 5

(14) 3-Step Coating

(15) Polymer beads as obtained in Example 1 (5 g) were re-dispersed in a 250 mL three-neck flask by addition of toluene (50 mL). Under slight stirring aluminum isopropoxide (0.01 g) and SiCl.sub.4 (0.5 mL) were added. After 12 h of stirring the supernatant was removed and the thus obtained coated polymer beads were washed with hexane and dried at 30° C. This procedure was repeated twice, in order to obtain polymer beads with three coating layers.

EXAMPLE 6

(16) Water-Retention Tests

(17) Coated polymer particles were prepared according to Example 3 and different thicknesses of the coatings were obtained by different numbers of coating cycle repetition. Separated test tubes were charged with the obtained particles (particle size: 100 to 200 μm, 1 g) and 10 mL of water (Merck Millipore) and the layer thickness was determined. Table 1 shows that increasing layer thickness provides increasing water retention times. Water retention time means that a contact between the water-swellable polymer core and surrounding water is prevented for a measured period of time.

(18) Water retention time measurement: 30 mg of coated particles were charged into a test tube together with 1 mL of water. Test tube was shaken until a gel was formed, indicating cracking of the SiO.sub.2 shell followed by swelling of SISA core. The time from shaking the test tube to gel formation which is observed visually is the water retention time.

(19) TABLE-US-00001 TABLE 1 Layer thickness [μm] Water retention time [min] 0.375 5 0.395 8 0.416 15 0.488 100

(20) Layer thickness of 0.375 μm already provides water retention of 5 min. Increasing the layer thickness to more than 400 μm provides water retention of 15 min (0.416 μm) or even 100 min (0.488 μm).

COMPARATIVE EXAMPLE

(21) A water-swellable polymer core was prepared according to the polymerization procedure of Example 3. However, no coating steps were carried out after the polymerization reaction. The resulting polymer core was purified by filtration, washing and drying. Said non-coated polymer core (layer thickness=0 μm) has been applied for a comparative experiment according to the procedure of Example 6. Said comparative experiment provided a water retention time of less than 1 min.

EXAMPLE 7

(22) Preparation of a Cationic Water-Swellable Polymer by Inverse Suspension Polymerization

(23) A 2 L double jacketed reactor was charged with 600 g of white spirit D40. After addition of 3 g Span 80 and 5.0 g of MUV the mixture was purged with nitrogen at a rotation speed of 300 rpm for 90 min. The aqueous monomer phase was prepared in a separate vessel. For this purpose, initially 23.3 g of water were introduced and 152.00 g (28 mol-%) of aqueous DIMAPA Quat solution (60 wt.-% solution in water), 161.30 g (72 mol-%) of acrylamide 50 wt.-% solution in water) and 4 g (0.03 mol-%) of aqueous methylene bisacrylamide solution (2 wt.-% solution in water) were added subsequently and neutralized with 7.93 g of a 50% sodium hydroxide solution, in order to adjust a pH of 6. Additionally, 3.60 g of an aqueous 4% V50 solution and 3.60 g of an aqueous 1% sodium bisulfite solution were added to the aqueous phase. This aqueous solution was combined with the oil phase in the reactor and the oil/water mixture was dispersed at a rotation speed of 300 rpm for 2 min. The polymerization was initiated by addition of 3.6 g of an aqueous 0.5% tert.-butyl hydroperoxide solution. The batch was stirred for 30 min. Subsequently, the water was azeotropically distilled off at 620 rpm, 50 mPa and 60° C. The polymer beads were filtered, washed with acetone and dried at 40° C. in a drying chamber for 6 hours.

EXAMPLE 8

(24) Preparation of Coated Polymer Particles by a Fluidized Bed Coating Process

(25) Water-swellable polymer particles containing 45.0% by weight of 2-acrylamido-2-methylpropanesulfonic acid, 5.0% by weight of acrylic acid, 49.9% by weight of acrylamide, and 0.2% by weight of methylenebisacrylamide were used.

(26) The following water glasses were used: Sodium water glass containing 8.8% Na.sub.2O, 28% SiO.sub.2 and 63.2 H.sub.2O; modulus 3.4; solids content 38.2%; Potassium water glass containing 12.5% K.sub.2O, 26.7% SiO.sub.2 and 60.8% by weight H.sub.2O; modulus 3.35; solids content 39.2%.

(27) The silica precursor solution was prepared by diluting the above mentioned water glass solutions with water (3 parts water glass, 1 part water). Afterwards, 62.5 wt % of a 0.5 M hydrochloric acid solution (compared to the amount of the formerly prepared solution) were carefully added.

(28) The water-swellable polymer particles (445 g) were placed into a fluidized bed apparatus (Co. Bosch Huetlin, Type Unilab 1) in which the particles were heated to 80° C. The silica precursor solution was then sprayed onto the particles (air inlet temperature: 80° C.; outlet temperature: 60° C.; gas volume: 160 m.sup.3/h; micro climate 0.12 bar; nozzle pressure: 0.55 bar). In total, 1300 g of the silica precursor were sprayed onto 445 g of the particles. Finally, silicate coated SISA particles were obtained.

EXAMPLE 9

(29) Water-swellable polymer particles as used in Example 8 (450 g) were placed into a fluidized bed apparatus (Co. Bosch Huetlin, Type Unilab 1) in which the particles were heated to 80° C. A silica precursor solution as used in Example 8 was then sprayed onto the particles (air inlet temperature: 80° C.; outlet temperature: 55° C.; gas volume: 160 m.sup.3/h; micro climate 0.15 bar; nozzle pressure: 0.55 bar). In total, 1300 g of the silica precursor were sprayed onto 450 g of the particles. After spraying of additionally 200 mL of water for homogenization and cleaning of the nozzles and tubbing, 500 mL of a 1 M hydrochloric acid was sprayed onto the particle at the same rate than before. Finally, silica coated water-swellable polymer particles were obtained.