Pyrrolidine-functionalized cyclocopolymers containing carboxylate-, sulfonate-, and phosphonate-pendants as acidizing corrosion inhibitors for mild steel: Experimental and theoretical insights

Mild steel corrosion under very acidic conditions remains a major problem in industrial operations. In this study, three pyrrolidine-functionalized cyclocopolymers containing different anionic pendants- sulfonate ( PS) , carboxylate ( PC) , and phosphonate ( PP) were synthesized and evaluated for mild steel corrosion in 15 wt.% HCl. 1 H and 13 C NMR, FTIR, and TGA were used to characterize the synthesized polymers, confirming their structures and high thermal stability. Gravimetric weight loss (WL), electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization (PDP) were used to evaluate corrosion efficacies. All three polymers markedly inhibited the corrosion of mild steel, exhibiting IEs of 77.2%, 81.5%, and 78.8% for PS , PC , and PP , respectively, at 298 K. The efficiencies remained stable at 333 K. Under optimal conditions, they exhibited excellent IEs of 94.5%, 96.1%, and 94.8%, respectively. Thermodynamic parameters obtained from adsorption studies ( ≤ – 40 kJ mol -1 , ΔH ≠ , and E a ) suggested that the inhibitors adsorb strongly on the metal surface, following the Langmuir isotherm, with predominant chemisorption. Surface analyses using SEM and XPS provided strong evidence for the adsorption of these inhibitors on the metal surface. Computational (DFT and MD) studies further support the experimental observations, revealing favorable adsorption energies and a flat orientation of the inhibitor molecules on the Fe(110) surface. A brief mechanistic discussion of how heteroatom-rich functional groups and the polymer architecture interact with the metal surface has also been provided.