Poly(Phenylenediamine): An effective polymer motif for anticorrosive applications

Phenylenediamine (C6H4(NH2)2) exists in three isomeric forms i.e. ortho-isomer (PoPD), metaisomer (PmPD) and para-isomer (PpPD). The o-phenylenediamine, m-phenylenediamine and p-phenylenediamine polymerized to give poly(o-phenylenediamine) (PoPD), poly(m-phenylenediamine) (PmPD) and poly(p-phenylenediamine) (PpPD), respectively. Literature investigation suggests that poly(phenylenediamines), specially poly(o-phenylenediamine) are widely employed as anticorrosive materials for different metals and alloys, especially in the sodium chloride and hydrochloric acid solutions. Because of their polymeric nature, PoPD, PmPD and PpPD provide excellent surface protection and exhibit excellent anticorrosive activity. They are extensively used as anticorrosive materials for different metals and alloys such as mild steel, carbon steel, aluminum, copper zinc etc. in different common electrolytes including sulfuric acid and hydrochloric acid. PoPD, PmPD and PpPD can interact with metal surface using their non-bonding electrons of nitrogen atoms and π-electrons of aromatic rings. Due to the presence of various electron rich adsorption sites, PoPD, PmPD and PpPD and their derivatives are expected to form a compact anticorrosive film on the metal surface. Their adsorption on metallic surface mostly follows the Langmuir adsorption isotherm model. Present review describes the assortment of present and past advancements on anticorrosive effect of PoPD, PmPD and PpPD. This article also aims to describe the corrosion inhibition mechanism of metals and alloys using PoPD, PmPD and PpPD.