Study of metal protective hydrophobic coatings from waterborne polyurethane ionomers

A series of waterborne coatings obtained from aqueous dispersions of fluorinated polyurethane ionomers were characterized by Differential Scanning Calorimetry (DSC), Contact Angle measurements (CA), and Electrochemical Impedance Spectroscopy (EIS) with evaluation of water uptake and barrier properties at prolonged exposure. All the considered materials showed two glass transition temperatures and the formation of highly hydrophobic surfaces with CA values against water well above 100 degrees. On the other hand the compositive parameters of the polymers-presence and concentration of cationic as well as anionic groups, linear or crosslinked molecular structure-showed a significant effect on the electrochemical behaviour. In particular it resulted that less water absorption is shown by coatings with lower ionic character, while crosslinked anionomer structures show excellent long-term barrier properties. The research offers useful indication towards the design of a new class of hydrophobic barrier coatings from aqueous dispersions.