Preparation and Properties of Poly(urethane-urea) Crosslinked Coatings from Perfluorocopolyethers and Polyfunctional Isocyanurates

Abstract

Two model isocyanate terminated resins were synthesized by addition of perfluorocopolyether oligomers (M̄n ca. 1 000) with cyclic polyisocyanurates of hexamethylene diisocyanate (HDI) and isophorone diisocyanate (IPDI). The resins were characterized by chemical titration, gel permeation chromatography, FT-IR spectroscopy, and viscosity. The two resins, and some blends of them, were crosslinked through urea bond formation by exposure to atmospheric moisture. The resulting coatings were characterized by dynamic mechanical spectroscopy (DMS), tensile properties, abrasion resistance, adhesion, atomic force microscopy (AFM) and contact angle measurements. Phase separation phenomena and mechanical properties were related to composition and thermal transitions of both hard and soft phase. Adhesion (pull-off) was poor on inorganic surfaces like glass and aluminium (<1 MPa) and good on organic primers (>5 MPa). The use of organosilane adhesion promoters was successfully investigated. Surface analysis by AFM showed the formation of a chemically heterogeneous very smooth (on a nanoscale) surface. Contact angle determinations with water, diiodomethane and hexadecane were carried out. The total surface energy of coatings was calculated by the harmonic mean approximation and resulted typically low (16.0–17.5 mN/m) and unaffected by the coating bulk composition.