Synthesis and Characterization of Waterborne Hyperbranched UV Cured Polyurethane-Silica Hybrid Coatings

Abstract

The third generation glycerol based hyperbranched polyester (HBPE-3G) was synthesized by reacting glycerol and 2, 2-bis(hydroxymethyl) propionic acid in a stoichiometric molar ratio. This polyester was used as preparation of waterborne hyperbranched UV cured polyurethane-silica hybrid coatings. The acrylic terminated waterborne coatings were prepared by modifying some of the hydroxyl groups HBPE-3G to acidic groups by reacting with maleic anhydride. The remaining hydroxyl groups were reacted with NCO terminated acrylate. Then the prepolymer was neutralized with triethyl amine and dispersed in water. The water based hybrid formulations were prepared by mixing 3, 5 and 10 % Trimethoxysilylpropyl Methacrylate (TMSPM or MEMO) into the acrylic terminated waterborne coatings. The films were casted and cured under UV light. The various film properties are studied by XRD, AFM, TGA and DMTA instruments. The TGA and DMTA results suggest an increase in the onset degradation temperature, final mass residue, storage modulus and glass transition temperature for the hybrid formulations. The structural characterization of the hybrid coatings was performed using FTIR and NMR spectroscopy. The tensile tests demonstrated that the mechanical properties improve with the increasing of TMSPM content. Surface morphologies were characterized by atomic force microscopy (AFM). AFM study revealed that TMSPM was crosslinked homogenously through the polymer matrix. The TGA and DMTA data suggest that higher thermal stability and glass transition temperature (Tg) for the TMSPM hybrid films compared to their pure counterparts and were increased with increasing the TMSPM content.