Salt-tolerant star macromolecules

1. A salt-tolerant star macromolecule, comprising:

i) a core;

ii) a plurality of hydrophilic polymeric arms; and

iii) at least one-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;

wherein;

1) the salt-tolerant star macromolecule, when dissolved in water at a concentration of at least 0.3 wt. % forms a homogeneous gel; and

2) the formed homogeneous gel has a dynamic viscosity at 80° C. that is at least 50% relative to viscosity of the gel at 25° C., according to the Temperature Stability Test.

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-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.

6. 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 oft 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.

7. 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.

8. 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.

9. 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.

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

11. 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; and

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.

12. The salt-tolerant star macromolecule of claim 1 , wherein the salt-tolerant star macromolecule, when dissolved in water a concentration of 0.4% wt. %, forms a homogenous gel; and has a dynamic viscosity of at least 20,000 cP at a pH between 5.5-11.

13. The salt-tolerant star macromolecule of claim 5 , wherein the monomeric residues of one or more polymerized salt-tolerant-enhancing monomers present within the salt-tolerant-enhancing polymeric segment comprise methyl acrylate or methyl methacrylate.

14. The salt-tolerant star macromolecule of claim 13 , wherein the monomeric residues of one or more polymerized hydrophobic monomers present within the salt-tolerant-enhancing polymeric segment comprise styrene.

15. A composition, comprising the salt-tolerant star macromolecule of claim 1 .

16. The composition of claim 15 , wherein the composition is an aqueous composition.

17. The composition of claim 16 , wherein the composition is a fracturing fluid composition.