Investigating the structure-to-property of thermo-thickening polymers capped by different structural side chains

This study investigates the structure and comparison of solution properties of a series of acrylamide-based polymers capped by different thermo-sensitive side chains such as N-vinyl caprolactam (NVCL), N,N-dimethylacrylamide (DEAM) and N-isopropylacrylamide (NIPAM) synthesized via continuous initiation free-radical polymerization. Techniques such as Fourier-transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance (1H NMR) afforded the chemical structure, X-ray diffraction (XRD) exhibit the tacticity and environmental scanning electron microscopy (ESEM) displayed the morphology. Turbidimetry, dynamic light scattering (DLS), and DSC techniques examined the responsiveness and hydrodynamic radii of the colloidal particles at their lower critical solution temperature (LCST). The thickening profiles were investigated via rheometric analysis and the relationship between viscoelastic properties and hydrodynamic radii synergistically explained the anomalous viscosity build-up among the different side chains. The polymers exhibited excellent thickening abilities at high temperatures (>70 °C) with relatively rough surface mixed intercalations attributed to the thermo-responsive moieties grafted on acrylamide methylpropane sulfonic acid (AMPS) as thermal resistance backbone. PAMPS/NVCL displayed particularly excellent responses owing to its partial conjugation effect, compared to PAMPS/DEAM and PAMPS/NIPAM in solution at 150 °C. The polymers also displayed strong anti-salt responses, with a drop in viscosity initially observed but quickly subdued due to hydrophobic side chain association, electrostatic shield, and double-layer compression of the hydrated shells. These polymer side chains grafted on acrylamide backbones promote excellent self-assembly properties at varying grafting ratios and are interesting as self-adaptive rheology modifiers and fluid immobilizers for enhanced oil and gas recovery in deep reservoirs.