Anti-corrosive properties of poly (2-pyridylamine-co-aniline-co-2,3-xylidine) terpolymer coating on mild steel in different corrosive environments

A soluble terpolymer from 2-pyridylamine (2PA), aniline (AN) and 2,3-xylidine (XY), poly (2PA-co-AN-co-XY) was synthesized by chemical oxidative polymerization using ammonium persulfate as an oxidant in hydrochloride aqueous medium. The two copolymers, poly (AN-co-XY) and poly (2PA-co-AN) were also synthesized by following identical synthesis route. The resultant terpolymer and copolymers were characterized by Fourier transform infrared (FTIR) and 1H NMR spectroscopy. The terpolymer and copolymers were chemically deposited on mild steel specimens using N-methyl-2-pyrrolidone (NMP) as solvent via solution evaporation method. The anticorrosive properties of terpolymer and copolymers coatings was investigated in major corrosive environments such as 0.1 M HCl, 5% NaCl solution, artificial seawater, distilled water and open atmosphere by conducting various corrosion tests which include: immersion test, open circuit potential measurements, potentiodynamic polarization measurements, and atmospheric exposure test. The corrosion performance of terpolymer and copolymers coatings was also compared separately with polyaniline (PANi) homopolymer coating. The surface morphology of terpolymer and copolymers coatings was evaluated using scanning electron microscopy (SEM). The synthesized terpolymer exhibited excellent protection against mild steel corrosion; the protection efficiency being in the range of 93–96% after 30 days of immersion. The corrosion performance of individual copolymers was found inferior than the terpolymer. However, the performance of copolymer poly (2AN-co-XY) was found better than copolymer poly (2PA-co-AN).

► Terpolymer poly (2-pyridylamine-co-aniline-co-2,3-xylidine) chemically synthesized.
► Terpolymer, its individual copolymers deposited on steel by solution evaporation.
► Anticorrosive properties of polymers examined in different corrosive environments.
► Corrosion tests include immersion, electrochemical and open atmospheric exposure.
► Excellent protection efficiency (93–96%) for terpolymer after 30 days of immersion.