Study On Assembly Of Functionalized Nano-Silica Sol With Polymers

Assembly of inorganic-organic hybrids and associated nanotechnology have taken great advantage of the synthesis of revolutionary nanocomposites and therefore aroused increasing attention among researchers. These novel materials can have unexpected properties such as mechanical, electrical, optical, magnetic and catalytic properties due to the synergism of the polymer matrix and the nanoinorganics. Recent progress in new polymer synthesis techniques makes it possible to fabricate well-defined polymer hybrid nanocomposites with novel properties and controlled architectures. There are two main methods for attaching polymer chains onto nanoparticle surfaces, including 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").Usually the preparation process of sol-gel consists of hydrolysis of metal alkoxides and the subsequent polycondensation. Also the reaction condition is mild and easy to control. Therefore, the sol-gel method becomes a desired way to carry out preparation of nanomaterials, and which the structure and properties of nanomaterials can be controlled. In this study, the sol-gel method combined with assembly is attributed to a new method to synthesizing polymer hybrid nanocomposites. A sysmetic research work has been done and succeeded in the synthesis of polyurethane (PU) hybrid nanocomposites containing modified TiO₂/SiO₂ by the "grafting to" approach. In an addition, frontal polymerization (FP) was used to synthesize PU/ SiO₂ sol hybrids primarily. Furthermore, the in situ assembly of functionalized silica sol with polymethacrylate and polystyrene was investigated respectively.Firstly, TiO₂/SiO₂ composite inorganic nanoparticles were prepared by sol-gel process. 3-aminopropyltriethoxysilane (APTS) was used modifying TiO₂/SiO₂ nanoparticles, and then the functionalized TiO₂/SiO₂ and PU were assembled formingwell-defined PU hybid nanocomposites (PU/TiO2-SiO2) by the aid of "grafting to" polymerization. The microstructure of TiCVSiCb nanoparticles was characterized by X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy. The structure and properties of PU/TiCh-SiCb hybrid films were characterized by FT-IR, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) respectively. It was shown that when the molar ration of Ti to Si reached 1:1, the assembly of titania with silica was completely achieved and the new bond Ti-O-Si was formed. The APTS was grafted onto the surface of TiCVSiCh nanoparticles and the APTS/TiOi-SiCh particles could be covalently bonded with polyurethane, which can form welldefined shell-core structure; the Ti(VSiO2 modified by APTS can disperse in PU matrix with keeping nanoscale size. The glass transition temperatures of hybrid nanocomposites PU/TiCVSiCh were slightly higher than that of pure PU.In addition, frontal polymerization was used to fabricate PU/SiO2 sol hybrids firstly. The effect factors of different molecular weights of polyether and different concentration of catalyst on frontal polymerization were totally investigated, along with comparison of frontal polymerization with batch polymerization (BP) in this paper. FT-IR, TEM, and TGA were employed to characterize PU hybrids. The results showed that the obtained polymer materials by FP displayed similar features such as infrared characteristic peaks and thermal stability compared with those obtained by BP. Nanosilica sol was well dispersed in the PU hybrid matrix even though no any stirring occurred during the FP process. The average size of silica sol in PU matrix is about 40nm.The assembly of functionalized silica sol with polymethacrylate and polystyrene was investaged respectively. The process of assembly of silica sol with polymethacrylate was measured by FT-IR, TGA, TEM and water contact angle analysis (WCA). It indicated that the silica hybrid sol contained acrylate function group which could be assembled with methacrlate monomers. The optimal concentration of silica on PMMA/SiCh hybrids, along with good thermal stability, is 0.5 wt%. The nanosilica sol hybrid modifed by silane could be dispersed at thenanoscale size since the modified silica sol was not easy to aggregate again and the hybrid silica sol was well compatible with PMMA matrix, which can form welldefined core-shell structure. The hydrophobic property of PMMA hybrids was enhanced with the increase of silica sol content. When the content of silica sol increased to 0.6 wt%, the water contact angle reached 92° and the minimum surface energy of hybrids reached 35.76dyn/cm, which was decreased by 32.43% compared to pure PMMA. Besides the process of assembly of silica sol with polystyrene was confirmed by FT-IR, TGA, SEM and WCA. It showed that the thermogravimetric rate of PS hybrids was relatively slow and represented' great thermal stability. The nanosilica sol modified by silane dispersed well in PS'matrix since the silica hybrid sol was not easy to aggregate and the hybrid sol was well'compatible with PS matrix. The average particle size of nanosilica sol in PS hybrids was about 80 nm. The hydrophobic property of PS hybrids was enhanced with the increase of silica sol content. When the content of silica sol increased to 0.5 wt%, the water contact angle reached 118° and the minimum surface energy of hybrids reached 19.31dyn/cm, which was decreased by 60.47% compared to pure PS. It can be drawn a conclusion that the hybrid nanosilica sol, which assembled in PMMA and PS matrix respectively, can greatly increase the hydrophobic properties of polymers.