Dual-mechanism thickening agents for hydraulic fracturing fluids

1. A star macromolecule represented by Formula (I):

wherein:

Core represents a crosslinked polymeric segment;

P1 represents a hydrophobic polymeric segment comprised predominantly of repeat units of monomeric residues of polymerized hydrophobic monomers;

P2 represents a hydrophilic polymeric segment comprised predominantly of repeat units of monomeric residues of polymerized hydrophilic monomers;

P3 represents a hydrophilic polymeric segment comprised predominantly of repeat units of monomeric residues of polymerized hydrophilic monomers;

P4 represents a hydroxyl-containing segment (homopolymeric or copolymeric) comprised of repeat units of monomeric residues, where at least one of the monomeric residues or a plurality of the monomeric residues is a hydroxyl-monomeric containing monomeric residue, of polymerized monomers;

P5 represents a hydrophilic polymeric segment comprised predominantly of repeat units of monomeric residues of polymerized hydrophilic monomers;

q1 represents the number of repeat units in P1 and has a value between 1 and 50;

q2 represents the number of repeat units in P2 and has a value between 30 and 2000;

q3 represents the number of repeat units in P3 and has a value between 30 and 2000;

q4 represents the number of repeat units in P4 and has a value between 1 and 50;

q5 represents the number of repeat units in P5 and has a value between 30 and 2000;

r represents the number of polymeric arms covalently attached to the Core;

s represents the number of hydroxyl-containing arms covalently attached to the Core; and

t represents the number of hydrophobic-containing copolymeric arms covalently attached to the Core; and

wherein:

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

ii) when t is at least 1:

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

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

c) combinations thereof.

2. The star macromolecule of claim 1 , wherein the star macromolecules has a molecular weight of between 150,000 g/mol and 5,000,000 g/mol.

3. The star macromolecule of claim 1 , wherein the sum total number of arms (r+t) is between 3 and 1000, or the sum total number of arms (s+t) is between 3 and 1000, or both sum total number of arms (r+t) and sum total number of arms (s+t) are each between 3 and 1000.

4. The star macromolecule of claim 1 , wherein the molar ratio of r to t is in the range of between 8:1 and 3:1, or the molar ratio of s to t is in the range of between 8:1 and 3:1, or both the molar ratio of r to t and the molar ratio of s to t are each in the range of between 8:1 and 3:1.

5. The star macromolecule of claim 1 , wherein:

i) both q2 and q3 have a value greater than 100, and q2 is greater than q3; or

ii) both q5 and q3 have a value greater than 100, and q5 is greater than q3; or

iii) both q2 and q3 have a value greater than 100, and q5 and q3 have a value greater than 100, and q2 and q5 are greater than q3.

6. The star macromolecule of claim 1 , wherein the core comprises a hydrophobic crosslinked polymeric segment.

7. The star macromolecule of claim 1 , wherein the star macromolecule is a water soluble mikto star macromolecule.

8. The star macromolecule of claim 1 , wherein the star macromolecule, when dissolved in water at a concentration of at least 0.2 wt. %, forms a clear, homogeneous gel having a viscosity of at least 20,000 cP .

9. A star macromolecule composition, comprising at least 0.05 wt. % of the star macromolecule of claim 1 .

10. The star macromolecule composition of claim 9 , wherein the composition is a fracturing fluid thickening additive, a drilling well fluid thickening additive, a gelling agent, or an additive to improve oil extraction from oil sands.

11. The star macromolecule composition of claim 10 , wherein the composition is a rheology-modifying composition having a shear-thinning value of at least 6.

12. The star macromolecule composition of claim 10 , wherein the composition further comprises one or more boric acid additives or borate-type additives.

13. The star macromolecule composition of claim 10 , wherein the composition comprises predominantly star macromolecules having a molecular weight within 5% of the molecular weight of the pre-determined star macromolecule represented by Formula (I), relative to the total star macromolecules in the composition.

14. A process of preparing a star macromolecule represented by Formula (I) of claim 1 , wherein the star macromolecule represented by Formula (I) is prepared by one or more star macromolecule processes, comprising: one-pot process, the arm first process, ATRP, CRP, RAFT, TEMPO, Nitroxide, LRP, anionic polymerization, cationic polymerization, or combinations thereof.

15. The star macromolecule of claim 1 , wherein:

i) r, s, or t, or the sum of r and t, or the sum of s and t, is greater than 3; and

ii) the star macromolecule, when dissolved in:

1) water at a concentration of at least 0.05 wt. %, forms a homogeneous gel having a viscosity of at least 20,000 cP, wherein the star macromolecule has a molecular weight of between 150,000 g/mol and 5,000,000 g/mol; and

2) a 0.2 wt. % Borax aqueous solution, forms a gel having an increase in dynamic viscosity of at least 5,000 cP, or an increase in dynamic viscosity of at least 12%, according to Borate-Crosslinker Thickening Test, relative to the dynamic viscosity of a homogeneuous gel of the star macromolecule with 0.0 wt. % Borax aqueous solution.

16. The star macromolecule of claim 15 , wherein the sum total number of arms (r+t) is between 3 and 1000, or the sum total number of arms (s+t) is between 3 and 1000, or both sum total number of arms (r+t) and sum total number of arms (s+t) are each between 3 and 1000.

17. The star macromolecule of claim 15 , wherein the molar ratio of r to t is in the range of between 8:1 and 3:1, or the molar ratio of s to t is in the range of between 8:1 and 3:1, or both the molar ratio of r to t and the molar ratio of s to t are each in the range of between 8:1 and 3:1.

18. A star macromolecule composition, comprising at least 0.05 wt. % of the star macromolecule of claim 15 .

19. The star macromolecule composition of claim 18 , wherein the composition is a fracturing fluid thickening additive, a drilling well fluid thickening additive, a gelling agent, or an additive to improve oil extraction from oil sands.

20. The star macromolecule composition of claim 19 , wherein the composition is a rheology-modifying composition having a shear-thinning value of at least 6.

21. The star macromolecule composition of claim 19 , wherein the composition further comprises one or more boric acid additives or borate-type additives.