Improvement of corrosion protection of steel by incorporation of a new phosphonated fatty acid in a phosphorus-containing polymer coating obtained by UV curing

tSix formulations containing diacrylate monomers (from 89 to 92.5% (w/w)) as well as a phosphonatedmethacrylate monomer (from 1 to 10% (w/w)) were prepared. All formulations were UV-cured and thecorrosion performance of the resulting coatings applied onto a steel substrate was assessed by elec-trochemical impedance spectroscopy (EIS). It was first shown that the coatings containing phosphonicacid methacrylate (MAPC1(OH)2) instead of methacrylate phosphonic dimethyl ester (MAPC1) presentedhigher corrosion protection related to the strong adhesive properties of phosphonic acid on the metalsubstrate. A minimum MAPC1(OH)2content of 2.5% was determined to provide the highest impedancevalues (best efficiency). Then, a new bio-based compound, i.e. phosphonic acid-bearing oleic acid (phos-phonated fatty acid), was synthesized and added as an inhibitor to the formulations. In the presence ofthis compound, the corrosion protection was notably improved. The beneficial effect of phosphonatedfatty acid was explained by its inhibitive action at the steel/coating interface and by the improvement ofthe barrier properties.