Salt-tolerant star macromolecules

1. A salt-tolerant star macromolecule, comprising:

i) a core;

ii) one or more hydrophilic polymeric arms; and

iii) one or more salt-tolerance-enhancing copolymeric arm, comprising:

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

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

iv) one or more copolymeric arms, comprising

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

b) a hydrophobic polymeric segment distal to the core.

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

3. 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.

4. The salt-tolerant star macromolecule of claim 1 , wherein the salt-tolerance-enhancing polymeric segment comprises:

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

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

5. The salt-tolerant star macromolecule of claim 4 , wherein the monomeric residues of one or more polymerized salt-tolerance-enhancing monomers present within the salt-tolerance-enhancing polymeric segment comprise methyl acrylate or methyl methacrylate.

6. The salt-tolerant star macromolecule of claim 4 , wherein the monomeric residues of one or more polymerized hydrophobic monomers present within the salt-tolerance-enhancing polymeric segment comprise styrene.

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-tolerance-enhancing polymeric segment comprising repeat units of:

a) monomeric residues of one or more polymerized salt-tolerance-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 1 to 1000;

s independently represents the number of salt-tolerance-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 1 to 1000; and

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

wherein the molar ratio of:

a) r to s is in the range of between 40:1 and 1:4, or

b) r to t is in the range of between 40:1 and 1:40, or

c) t to s is in the range of between 40:1 and 1:40, or

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

e) combinations thereof.

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 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.

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

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

13. The composition of claim 12 , wherein the composition is an aqueous composition.

14. The composition of claim 13 , wherein the composition is a fracturing fluid composition.