Castor Oil based Poly(urethane-co-pyrrole)s as Novel Electroactive Anticorrosive Coatings for Steel

In recent years, several studies have been reported on use of conducting polymers as anticorrosive materials. But low processability and inferior mechanical properties are main drawbacks of these materials for surface coating applications. In order to overcome these difficulties, in the present work novel block copolymers of polypyrroles (PPy) and polyurethanes with high flexibility and mechanical properties similar to pure polyurethanes and conductivity close to pristine PPy were prepared. For this purpose, a hydroxyl terminated polyurethane prepolymer was prepared by the reaction of castor oil, isophorone diisocyanate and butane diol. This compound was used as initiator for oxidative polymerization of pyrrole in the presence of different amounts of cerric ammonium nitrate as catalyst. The structures of the prepared copolymers were confirmed by examination of their FTIR and 1HNMR spectra. Different formulations of copolymers with difference conductivity were prepared by changing molar ratio of reactants. In contrast to PPy homopolymer, the prepared copolymers were readily soluble in common organic solvents such as acetonitrile and N,Ndimethylformamide mixture. The protective anticorrosive coatings were readily obtained by electrochemical deposition of copolymers from their solution on steel as working electrode by cycling continuously the potential between -0.8 and 1.8 V versus Ag/AgCl reference electrode at a potential scan rate of 0.03 V/s. Corrosion potential (Ecorr), polarization resistance (Rp) and corrosion current (Icorr) were main parameters that evaluated for coated steel. According to Tafel plot data the steel electrode coated with copolymer with highest conductivity (0.18 S/cm) showed much higher Ecorr (0.254v) and Rp (43 kΩcm2) values and lower Icorr value than uncoated steel electrode. Therefore, synthesized copolymers can be considered as effective anticorrosive coating for steel with about 0.6 V shift of corrosion potential.

کلیدواژه ها:

Castor Oil ، Polypyrrole ، Electrodeposition ، corrosion