Synthesis and Characterization of Hyperbranched Polyurethane−Urea/Silica Based Hybrid Coatings

A series of organic−inorganic hybrid coatings from hyperbranched polyurethanes (HBPU) were prepared using hyperbranched polyester and 3-aminopropyltriethoxysilane. Initially, isocyanate terminated HBPU prepolymers were synthesized from hyperbranched polyesters [prepared by the reaction of 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) with pentaerythritol, TMP, or glycerol as core moiety] with isophorone diisocyanate at NCO/OH ratio of 1.6:1 for 5 h at 70−80 °C. The partial excess NCO content of this prepolymer was reacted with 3-aminopropyltriethoxysilane in different concentrations. The remaining excess NCO completely reacted with atmospheric moisture. Fourier transform infrared (FTIR) spectroscopy was used for the structural analysis of HBPU hybrid coatings. Deconvolution of the FTIR spectra using Origin 6.0 software through Gaussian curve-fitting method was used to find out the changes and types of intermolecular H-bonding interactions in the hybrid films with the variation in concentration of sol−gel precursors added. The viscoelastic properties of the synthesized coatings were determined by dynamic mechanical thermal analysis (DMTA).