Fluoropolyether coatings: Relationships of electrochemical impedance spectroscopy measurements, barrier properties, and polymer structure

Ten model coatings, selected and obtained from a family of fluorinated resins synthesized by the reaction of perfluoroether oligomeric diols of different molecular weights with polyisocyanurates of hexamethylenediisocyanate (HDI) and isophoronediisocyanate (IPDI), were characterized with differential scanning calorimetry, mechanical testing, and electrochemical impedance spectroscopy measurements. The electrochemical and chemico-physical measurements show that the glass-transition temperature of the starting isocyanate trimers greatly influences the properties of the final urethane coatings; the IPDI trimer gives harder coatings with lower water permeabilities than the corresponding HDI-based materials. Moreover, for each class of materials (from IPDI or HDI), the fluorine content plays a relevant role: the higher the fluorine percentage, the lower the water absorption into the coatings. Furthermore, the chain length of the polyols used for the synthesis of the prepolymers is a variable that exhibits great influence on the coating properties: coatings containing shorter perfluoropolyether segments show better barrier properties. (C) 2001 John Wiley & Sons, Inc.