Polyurethane-Polysiloxane Ceramer Coatings

Abstract

New low VOC (volatile organic compounds) poly-urethane/oligosiloxane coatings were formulated using, 1, 6-hexamethylene diisocyanate (HDI) isocyanurate, alkoxysilane-functionalized HDI isocyanurate, tetraethyl orthosilicate (TEOS) oligomers and three cycloaliphatic polyesters. One series of polyester was synthesized using 1,4-cyclohexanedimethanol (CHDM) with 1,4-cyclohexanedicarboxylic acid (1,4-CHDA) and 1,3-cyclohexanedicarboxylic acid (1,3-CHDA). A second series of polyesters was synthesized using 2-butyl-2-ethyl-1,3-propanediol (BEPD) with 1,4-CHDA or 1,4-CHDA and 1,3-CHDA, respectively. The polyurethane provided the required mechanical properties and polysiloxane functioned as an adhesion promoter and a corrosion inhibitor. The continuous organic polyurethane phase was coupled to the inorganic polysiloxane phase via the alkoxysilane-functionalized HDI isocyanurate. The general coatings, tensile, viscoelastic properties, and corrosion resistance were evaluated for the ceramer coatings as functions of the polyester and concentration of TEOS oligomers. The coatings properties were dominated by the organic phase. The corrosion resistance was found to be a function of TEOS with a maximum of corrosion resistance and coating properties at 10-15 wt % TEOS. The film morphology was investigated using the combination of SEM (Scanning Electron Microscope) and X-ray analysis. Phase separation was observed for ceramer coatings resulting in SiO 2 particles. The size of the pre-ceramic silicon-oxo-particles was controlled by the Tg of the organic phase and the concentration of TEOS oligomers.