Preparation And Surface Grafting Modification Of Spherical Silica

In this study, the inorganic nano-silica (SiO2) spherical particles were prepared by the hydrolysis of tetraethyl orthosilicate (TEOS). Also, polymer/SiO2 organic-inorganic nanocomposite spheres with core-shell morphology were obtained via atom transfer radical polymerization, grafting methyl methacrylatethe (MMA) from the surface of silica without eliminating oxygen. All the contents and results are as follows:(1) Nano-silica spherical particles were prepared by using TEOS as silica source, ethanol as solvent and ammonia as catalyst, which was called the St?ber method. The size of nano-silica was changed with the reaction conditions, such as reaction temperature, catalyst and the amount of water, etc. Thus, the silica particles with different sizes can be obtained by altering the factors. Effects of amount of water, ammonia and TEOS, as well as temperature of hydrolysis on the particle sizes of silica were studied. The results of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that the nano-silica particles were spherical structure with particle size range between 190 and 250 nm. In addition, thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FT-IR) showed that a small amount of water was adsorbed on the silica. The decrease of quality of silica can be attributed to the loss of adsorbed water and the dehydration between silanols under high temperature.(2) The silanols (Si–OH) on the surface of silica were converted to amino groups (Si–NH2) by the reaction between the silanols and the aminopropyl triethoxysilane (APTES) in toluene solvent. And the amino groups could keep on reacting with 2-bromo isobutyrate bromide to produce initiator, which containing bromine atoms on the end of silica particles. Then the nanocomposites of poly(methyl methacrylate) and silica with core-shell structure were obtained in the presence of limited amount of air. The reactions were carried out without any deoxygenation and the method involved the polymerization of MMA with Cu(?) as the catalyst, pentamethyl diethylenetriamine (PMDETA) as ligand and ascorbic acid (VC) as reducing agent. The amount of reducing agent was calculated, based on the amount of catalyst and the residual volume of ampoule after the reaction solution added. The results of SEM and TEM confirmed that the composite microspheres were core-shell structure, and the diameter of the particles was larger than that of the initial silica. (3) The nanocomposites of PMMA/silica with core-shell structure were prepared by using 2-bromoisobutyryl bromide-functioned silica particles (Si–Br) as initiator, ferric chloride as catalyst and triphenylphosphine as ligand. PMMA could be grafted from the surface of silica in the presence of excess reducing agent and very little catalyst, without calculating the amount of air. The results of SEM and TEM indicated that the composite microspheres were core-shell structure, and the diameter of particles was larger than that of the initial silica. In addition, the results of TGA showed that the composites had a weight loss around 17%.