Study On Assembly Of Polyurethane/nanosilica Hybrids

Assembly of inorganic-organic hybrids and associated nanoscience have taken great advantage for the synthesis of revolutionary polymer nanocomposites and therefore aroused increasing interest among researchers. These novel materials can have unexpected properties such as mechanical, electrical, optical, magnetic and catalytic properties arising from the synergism of the polymer matrix and the nanomaterials. Recent progress in new polymer synthesis techniques makes it possible to synthesize well-defined polymer hybrid nanocomposites with novel properties and controlled architectures. There are many methods for attaching polymer chains onto nanoparticle surfaces, including chemisorption, covalent attachment of end-functionalized polymers to a reactive surface ("grafting to"), and in-situ monomer polymerization with monomer growth of polymer chains from immobilized initiators ("grafting from"). Of these hybrid nanocomposites, polyurethanes (PUs), as the organic matrix, have received most attention for their versatile properties and a variety of starting materials.In previous reports some research groups have prepared PU hybrid nanocomposites containing polyhedral oligomeric silsesquioxane (POSS) or silica prepared by sol-gel method. However it still remains relatively unexplored with respect to the preparation of PU hybrid nanocomposites by incorporating surface functionalized silica nanoparticles building blocks into a PU matrix. In this paper plenty of research work has been done and succeeded in the synthesis of PU hybrid nanocomposites containing modified silica by the "grafting to" approach. In this study the organic silicon compound 3-aminopropyltriethoxysilane (APTS) was used for the modification of nanosilica and then the functionalized silica (SIAP) and PU were assembled forming well-defined PU hybid nanocomposites (SIAP/PU) by the aid of "grafting to" polymerization. The structure and properties of SIAP/PU hybrid nanocomposites were characterized by Fourier transform infrared spectroscopy(FT-IR), transmission electron microscope (TEM), scanning electron microscope (SEM), differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), wide-angle X-ray diffraction (WAXD), tensile measurements and contact angle measurements. It was shown that the APTS was grafted onto the surface of the nanosilica and the SIAP could be covalently bonded with polyurethane, forming well designed shell-core structure; the nanosilica modified by APTS dispersed at the dimension of nanoscale since the SIAP was not easy to agglomerated again and the SIAP was well compatible with PU matrix due to the surface functionality onto nanosilica by the convalentle grafted APTS; the glass transition temperatures of hybrid nanocomposites SIAP/PU were slightly higher than that of pure PU; the incorporation of nanosilica greatly improved the mechanical properties of the hybrid nanocomposites SIAP/PU as compared to the pure polyurethane and with the increase contents of nanosilica in the hybid nanocomposites the tensile strength and elongation at break were also increased; the well assembled hybrid nanocomposite SIAP/PU displayed hydrophobic properties at the very small silica contents as compared with pure polyurethane resulting from the decrease of hydrophilic silanol groups; compared with the solid nanosilica, the nanosilica dispersed well in methyl ethyl ketone displayed relatively better dispersion in polyurethane matrix at the average diameter of 10-20nm though the silica content reached 10%weight; the hybrid prepared by epoxy resin(E44) blended with hybrid nanocomposite SIAP/PU exhibited better toughness and tenacity as compared with pure epoxy resin.