Electronic effects on protective mechanism of electropolymerized coatings based on N-substituted aniline derivatives for mild steel in saline solution

•Aniline derivatives with electron-donation and -withdrawal groups are electropolymerized on mild steel.•Electroactivity of coatings is recognized by apparent current density.•Anodic protection and physical barrier jointly contribute to anticorrosion effect.•Substituents enhance barrier effect of coatings.•Formyl favors electron delocalization along polymer backbone and improve anodic protection effect.