Electrochemical corrosion protection studies of aniline-capped aniline trimer-based electroactive polyurethane coatings

In this paper, the successful preparation of electroactive polyurethane (EPU) coatings containing amine-capped aniline trimer (ACAT) is presented for the first time. To accomplish this, ACAT was synthesized by carrying out oxidative coupling reactions between aniline and para-phenylenediamine, after which it was characterized through Fourier-transformation infrared and UV–vis spectroscopy. Subsequently, a polyurethane (PU) prepolymer was prepared by polymerizing diisocyanate of 4,4-methylene-bis(cyclohexylisocyanate), diol of polycaprolactone, and triol of phloroglucinol at 60 °C for 3 h. EPU was then produced by allowing the as-prepared polyurethane prepolymer to react with ACAT under suitable conditions. Non-electroactive polyurethane (NEPU) coating was also prepared for the control experiments. Based on a series of electrochemical corrosion measurements, EPU in the form of a coating was found to possess a clearly enhanced corrosion protection effect when compared to PU. The observed enhancement of the anticorrosion effect of EPU on a metallic substrate when compared to that of NEPU may have been caused by the redox catalytic capability of ACAT present in EPU, inducing the formation of a densely passive metal oxide layer (i.e., Fe2O3 and Fe3O4), as indicated by the results of scanning electron microscopy and electron spectroscopy for chemical analysis. The redox behavior of the EPU coatings was further analyzed and compared to that of the NEPU coating by cyclic voltammetric (CV) studies.