Salt-tolerant star macromolecules

1. A salt-tolerant star macromolecule that when dissolved in water at a concentration of at least 0.3 wt. % forms a homogeneous gel and has a dynamic viscosity of at least 10,000 cP in a 0.4 wt. % NaCl aqueous solution, according to the Salt Tolerance Test;

wherein the salt-tolerant star macromolecule comprises a plurality of polymeric arms comprising at least two types of arms, wherein:

i) a first polymeric arm that extends beyond a second polymeric arm; and

ii) the first polymeric arm has a salt-tolerant-enhancing segment on its distal end.

2. The salt-tolerant star macromolecule of claim 1 , wherein the salt-tolerant star macromolecule has a dynamic viscosity in a NaCl-containing aqueous solution that is greater than the dynamic viscosity at 0.0 wt. % NaCl aqueous solution, according to the Salt Tolerance Test.

3. The salt-tolerant star macromolecule of claim 1 , wherein the salt-tolerant star macromolecule has an increase in dynamic viscosity with an increase in NaCl concentration, according to the Salt Tolerance Test.

4. The salt-tolerant star macromolecule of claim 1 , wherein the dynamic viscosity of the salt-tolerant star macromolecule in a 0.2 wt. % NaCl aqueous solution is at least 40% of the dynamic viscosity at 0.0 wt. % NaCl aqueous solution, according to the Salt Tolerance Test.

5. The salt-tolerant star macromolecule of claim 1 , wherein the salt-tolerant star macromolecule comprises:

i) a core;

ii) the first polymeric arm is a salt-tolerant-enhancing copolymeric arm, comprising:

a) a hydrophilic polymeric segment proximal to the core; and

b) a salt-tolerant-enhancing polymeric segment distal to the core; and

iii) the second polymeric arm is a hydrophilic polymeric arm.

6. The salt-tolerant star macromolecule of claim 5 , wherein the salt-tolerant-enhancing polymeric segment comprises:

i) repeat units of monomeric residues of one or more polymerized salt-tolerant-enhancing monomers; and

ii) optionally, repeat units of monomeric residues of one or more polymerized hydrophobic or hydrophilic monomers.

7. The salt-tolerant star macromolecule of claim 1 , wherein the salt-tolerant star macromolecule is represented by Formula Z:

wherein:

Core represents a crosslinked polymeric segment;

P1 represents a hydrophilic polymeric segment comprised of repeat units of monomeric residues of one or more polymerized hydrophilic monomers;

P2 independently represents a salt-tolerant-enhancing polymeric segment comprising repeat units of:

a) monomeric residues of one or more polymerized salt-tolerant-enhancing monomers; and

b) optionally, monomeric residues of one or more polymerized hydrophobic or hydrophilic monomers;

P3 independently represents a hydrophilic polymeric segment comprised of repeat units of monomeric residues of one or more polymerized hydrophilic monomers;

P4 represents a hydrophobic polymeric segment comprised of repeat units of monomeric residues of one or more polymerized hydrophobic monomers;

P5 represents a hydrophilic polymeric segment comprised of repeat units of monomeric residues of one or more polymerized hydrophilic monomers;

q1 represents the number of repeat units in P1 and has a value between 10 and 2000;

q2 independently represents the number of repeat units in P2 and has a value between 10 and 500;

q3 independently represents the number of repeat units in P3 and has a value between 10 and 2000;

q4 represents the number of repeat units in P4 and has a value between 10 and 500;

q5 represents the number of repeat units in P5 and has a value between 10 and 2000;

r represents the number of polymeric arms covalently attached to the Core and has a value in the range of from 0 to 1000;

s independently represents the number of salt-tolerant-enhancing copolymeric arms covalently attached to the Core and has a value in the range of from 1 to 1000;

t represents the number of copolymeric arms covalently attached to the Core and has a value in the range of from 0 to 1000; and

n represents the number of salt-tolerant-enhancing arm types covalently attached to the Core and has a value of at least 1;

wherein:

i) the molar ratio of:

a) r to s is in the range of between 40:1 and 1:40;

b) the molar ratio of r to t is in the range of between 40:1 and 1:40;

c) the molar ratio of t to s is in the range of between 40:1 and 1:40;

d) the molar ratio of r to (s+t) is in the range of between 40:1 and 1:40; or

e) combinations thereof; and

ii) r and t cannot both equal zero unless n represents a value of at least 2.

8. The salt-tolerant star macromolecule of claim 1 , wherein the salt-tolerant star macromolecule has a molecular weight (Mn) in the range of from 5,000 g/mol to 10,000,000 g/mol.

9. The salt-tolerant star macromolecule of claim 1 , wherein the arms of the salt-tolerant star macromolecule independently have a molecular weight (Mn) in the range of from 1,000 g/mol to 250,000 g/mol.

10. The salt-tolerant star macromolecule of claim 7 , wherein the monomeric residues of one or more polymerized hydrophobic or hydrophilic monomers are present in the salt-tolerant-enhancing polymeric segment P2.

11. The salt-tolerant star macromolecule of claim 1 , wherein the salt-tolerant star macromolecule comprises a plurality of polymeric arms comprising at least three types of arms, wherein:

i) the first polymeric arm extends beyond the second polymeric arm and said first polymeric arm has the salt-tolerant-enhancing segment on its distal end; and

ii) a third polymeric arm that extends beyond said second polymeric arm and said third polymeric arm has a hydrophobic segment on its distal end.

12. The salt-tolerant star macromolecule of claim 1 , wherein the dynamic viscosity of the salt-tolerant star macromolecule at 80° C. is at least 50% relative to viscosity of the gel at 25° C., according to the Temperature Stability Test.

13. The salt-tolerant star macromolecule of claim 1 , wherein the dynamic viscosity of the salt-tolerant star macromolecule at 60° C. is at least 60% relative to viscosity of the gel at 25° C., according to the Temperature Stability Test.

14. A salt-tolerant thickening agent, comprising the salt-tolerant star macromolecule of claim 1 .

15. A method of making a salt-tolerant composition, comprising:

adding the salt-tolerant star macromolecule of claim 1 , that when dissolved in water at a concentration of at least 0.3 wt. % forms a homogeneous gel and has a dynamic viscosity of at least 10,000 cP in a 0.4 wt. % NaCl aqueous solution, according to the Salt Tolerance Test.

16. A method of making an aqueous composition salt-tolerant, comprising:

adding at least 0.3 wt. % of the salt-tolerant star macromolecule of claim 1 to the aqueous composition;

wherein the salt-tolerant star macromolecule when dissolved in water at a concentration of at least 0.3 wt. % forms a homogeneous gel and has a dynamic viscosity of at least 10,000 cP in a 0.4 wt. % NaCl aqueous solution, according to the Salt Tolerance Test.

17. The salt-tolerant star macromolecule of claim 7 , wherein the monomeric residues of one or more polymerized salt-tolerant-enhancing monomers present within the salt-tolerant-enhancing polymeric segment P2 comprises:

methyl acrylate, methyl methacrylate, methyl ethacrylate, ethyl acrylate, ethyl methacrylate, ethyl ethacrylate, n-butyl acrylate, n-butyl methacrylate, n-butyl ethacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, 2-ethylhexyl ethacrylate, N-octyl acrylamide, 2-methoxyethyl acrylate, 2-hydroxyethyl acrylate, N,N-dimethylaminoethyl acrylate, N,N-dimethylaminoethyl methacrylate, acrylic acid, methacrylic acid, N-t-butylacrylamide, N-sec-butylacrylamide, N,N-dimethylacrylamide, N,N-dibutylacrylamide, N,N-dihydroxyethyllacrylamide 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, benzyl acrylate, 4-butoxycarbonylphenyl acrylate, butyl acrylate, 4-cyanobutyl acrylate, cyclohexyl acrylate, dodecyl acrylate, 2-ethylhexyl acrylate, heptyl acrylate, iso-butyl acrylate, 3-methoxybutyl acrylate, 3-methoxypropyl acrylate, methyl acrylate, N-butyl acrylamide, ethyl acrylate, methoxyethyl acrylate, hydroxyethyl acrylate, diethyleneglycolethyl acrylate, 2-fluoroethyl acrylate, or 2-fluoroethyl methacrylate.

18. The salt-tolerant star macromolecule of claim 7 , wherein the monomeric residues of one or more polymerized salt-tolerant-enhancing monomers present within the salt-tolerant-enhancing polymeric segment P2 comprises:

methyl acrylate or methyl methacrylate.

19. The salt-tolerant star macromolecule of claim 10 , wherein the monomeric residues of the one or more polymerized hydrophobic or hydrophilic monomers monomers is present in the salt-tolerant-enhancing polymeric segment P2 and comprises:

styrene, methyl acrylate, ethyl acrylate, n-butyl acrylate, iso-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, decyl acrylate, octyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, iso-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, decyl methacrylate, methyl ethacrylate, ethyl ethacrylate, n-butyl ethacrylate, iso-butyl ethacrylate, t-butyl ethacrylate, 2-ethylhexyl ethacrylate, decyl ethacrylate, 2,3-dihydroxypropyl acrylate, 2,3-dihydroxypropyl methacrylate, 2-hydroxypropyl acrylate, hydroxypropyl methacrylate, glycidyl methacrylate, glycidyl acrylate, acrylamide, styrene, or styrene optionally substituted with one or more C1-C12 straight or branched chain alkyl groups.

20. The salt-tolerant star macromolecule of claim 10 , wherein the monomeric residues of the one or more polymerized hydrophobic monomers present in the salt-tolerant-enhancing polymeric segment P2 comprises styrene.