Hydrophobic, transparent waterborne UV-curable polyurethane nanocomposites based on polycarbonate and PCL-PDMS-PCL reinforced with colloidal silica

Waterborne ultraviolet-curable polyurethane (WUPU) and its nanocomposites based on polycarbonate and α,ω-dihydroxy-[poly(ε-caprolactone)-poly(dimethylsiloxane)-poly(ε-caprolactone)] (PCL-PDMS-PCL) were synthesized using isophorone diisocyanate (IPDI), dimethyl propionic acid (DMPA), polycarbonate diol (PCD), PCL-PDMS-PCL, hydroxyethyl methacrylate (HEMA), and aqueous colloidal silica. The resulting WUPU materials were characterized by Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopies, dynamic light scattering (DLS), and rheometry. The effects of PCL-PDMS-PCL and silica on the colloidal, physicochemical, and surface properties of the WUPU and its nanocomposites were studied. It was found that incorporation of PCL-PDMS-PCL (10 wt%) significantly enhanced the Young’s modulus, tensile strength, surface hydrophobicity, and water resistance of the WUPU films due to microphase separation and better interfacial adhesion between the PDMS soft phase and urethane hard phase provided by the PCL blocks. Furthermore, incorporation of silica (10 wt%) further improved the modulus, tensile strength, and water resistance of the PCD-PCL-PDMS-PCL-WUPU films without degrading the high surface hydrophobicity or transparency, due to the homogeneous dispersion and network structure of the silica clusters in the WUPU matrix.