The synthesis of poly(acrylic acid-co-acrylamide) was investigated to enhance its rheological properties. Syntheses were conducted in both aqueous and supercritical fluid media, with and without the incorporation of a novel star-shaped macromonomer. The macromonomer, synthesized from a Boltorn H30 core with PEGMA⁵⁰⁰ arms and modified to contain a single vinyl group, was copolymerized with acrylic acid and acrylamide. Comprehensive polymer characterization was performed using FTIR, NMR, and SEC-MALS-dRI techniques. Rheological assessments revealed that copolymers containing the star-shaped monomer exhibited significantly higher viscosities than those lacking the hyperbranched component, a result attributed to the inter- and intrachain interactions facilitated by the PEGMA⁵⁰⁰ arms. Additionally, purification studies demonstrated that dialysis was necessary to remove short-chain polymers, particularly for samples synthesized in supercritical media, to achieve optimal rheological performance. Polymers synthesized in a supercritical CO₂–ethyl acetate mixture exhibited higher viscosities compared to their water-synthesized counterparts. The integration of the novel star-shaped macromonomer into HPAM-like polymers offers substantial potential for enhanced oil recovery applications.

The development of associative polymers remains a critical challenge for enhanced oil recovery, where macromolecular stability must be maintained under thermal and saline stresses. In this study, a multiscale analysis of the structure–property relationship is conducted for poly(acrylamide-co-acrylic acid) (HPAM) copolymers modified with three hyperbranched architectures: Behera’s Amine (dendron), Boltorn H30 (hyperbranched aliphatic polyester), and Tannic Acid (polyphenolic pseudo-dendrite). Rheological evaluations reveal that while all associative copolymers outperform HPAM, their performance is governed by a complex interplay of bond energy and conformational exposure rather than molar mass alone. Tannic Acid-HPAM exhibit the greater viscosifying performance across varying pH, salinity, and temperature, because of its high-energy π–π stacking and phenolic hydrogen bonding. While Boltorn H30 showed superior thermal resistance due to its sterically confined hyperbranched architecture; Behera’s Amine analogues exhibited the lowest thermal resistance due to the dissociation of low-energy tert-butyl clusters. Molecular dynamics simulations provide a foundation for these findings, identifying solvent-accessible surface area as a primary predictor of network efficiency. Results demonstrate that Tannic Acid systems adopt conformations maximizing the exposure of interaction sites, facilitating transient intermolecular networks. This study establishes a guide for designing associative architecture, highlighting the synergy between bond energy hierarchy and conformational availability as essential for the next-generation EOR polymers.