Methods of making acrylamide-acrylic acid copolymers
A method of making acrylamide-acrylic acid copolymers in water-in-oil latices is described. The method results in a copolymer having randomly distributed carboxylate functionalities and is suitable for ionic crosslinking. The copolymers and their ionically crosslinked counterparts are useful for enhanced oil recovery processes.
1. A composition comprising a water-in-oil latex, the water-in-oil latex comprising a water phase and an oil phase, the water phase comprising water, acrylamide, and acrylic acid and having a pH of about 3.0 to 4.5; wherein the latex further comprises a surfactant mixture consisting essentially of nonionic surfactants and comprising a block copolymer.
2. The composition of claim 1 wherein the water phase consists essentially of water, acrylamide, and acrylic acid, wherein the pH of the water phase is about 3.0 to 4.5.
3. The composition of claim 1 wherein the ratio of acrylamide to acrylic acid is about 60:40 to 99:1.
4. The composition of claim 1 wherein the block copolymer is a triblock copolymer comprising at least one block consisting essentially of ethylene glycol repeat units and having an HLB of about 4 to 6.
5. The composition of claim 4 wherein the triblock copolymer further comprises at least one block consisting essentially of hydroxyacid repeat units.
6. The composition of claim 5 wherein the hydroxyacid is 12-hydroxystearic acid.
7. The composition of claim 1 wherein the pH is about 3.5 to 4.0.
8. A composition comprising a water-in-oil latex formed by a method comprising
a. combining water and monomers to form a water phase, the monomers comprising acrylamide and acrylic acid;
b. adjusting the pH of the water phase to between about 3.0 to 4.5;
c. combining a hydrocarbon solvent with a surfactant mixture to form an oil phase, the surfactant mixture consisting essentially of nonionic surfactants and comprising a block copolymer;
d. contacting the water phase and the oil phase to form a water-in-oil latex;
e. polymerizing the monomers to form a copolymer; and
f. neutralizing the water phase.
9. The composition of claim 8 further comprising the product of diluting the composition with a water source after neutralizing, wherein the copolymer concentration after diluting is about 0.01 wt % to 1.00 wt %.
10. The composition of claim 9 wherein the water source comprises water and a salt of Ca 2+ , Fe +2 , Fe +3 , Mg 2+ , Cr 2+ , Cr 3+ , Zn 2+ , or Al 3+ .
11. The composition of claim 10 wherein the salt is aluminum citrate or chromium acetate.
12. The composition of claim 8 wherein the ratio of acrylamide to acrylic acid units in the copolymer is about 50:50 to 99:1.
13. The composition of claim 8 wherein the neutralizing comprises contacting the composition with sodium hydroxide and an alkanolamide surfactant.
14. The composition of claim 13 wherein the alkanolamide surfactant is N,N-diethanololeamide.
15. A method of making a water-in-oil copolymer latex, the method comprising
a. combining water and monomers to form a water phase, the monomers comprising acrylamide and acrylic acid;
b. adjusting the pH of the water phase to between about 3.0 to 4.5;
c. combining a hydrocarbon solvent with a surfactant mixture to form an oil phase, the surfactant mixture consisting essentially of nonionic surfactants and comprising a block copolymer;
d. contacting the water phase and the oil phase to form a water-in-oil latex;
e. polymerizing the monomers to form a copolymer; and
f. neutralizing the water phase.
16. The method of claim 15 further comprising diluting the latex with a water source after neutralizing, wherein the copolymer concentration after diluting is about 0.01 wt % to 1.00 wt %.
17. The method of claim 16 wherein the water source comprises water and a salt of Ca 2+ , Mg 2+ , Cr 2+ , Cr 3+ , Zn 2+ , or Al 3+ .
18. The method of claim 17 wherein the salt is aluminum citrate or chromium acetate.
19. The method of claim 15 wherein the neutralizing comprises contacting the composition with a neutralizing solution, the neutralizing solution comprising sodium hydroxide and an alkanolamide surfactant.
20. A method of diluting a water-in-oil copolymer latex, the method comprising adding a water source to the water-in-oil copolymer latex of claim 15 after the neutralizing, wherein the water source comprises water and a salt of Ca 2+ , Mg 2+ , Cr 2+ , Cr 3+ , Zn 2+ , or Al 3+ ; and the copolymer concentration after diluting is about 0.01 wt % to 1.00 wt %.