Studies On Grafting Polymers Onto The Surface Of Silica Nanoparticles Via ATRP And Its Applications

Silica nanoparticle possesses marked small-dimension effect and surface effect, so it is widely used in plastics, rubber, coating, catalyst, biomedicine and other fields. Polymer/ nano silica composites combine the merits of the inorganic nanoparticles and polymer, displaying good application foreground. Atom transfer radical polymerization (ATRP) adapts to a lot of monomers and can control molecular weight and molecular weight distribution of grafted-polymer, providing a powerful tool for grafting polymers from silica nanoparticles surface. All these facts are the origin and impetus of this thesis, we had studied grafting polymers onto the surface of silica nanoparticles via ATRP and its application in this paper. The main results are shown as follows:1. A Stober Sol-gel method had been used to prepare monodisperse and uniform–size about 40 nm silica nanoparticles, and they were modified by silicane coupling agent KH-550. Then nano silica particles with ATRP initiator (SiO2-Br) were synthesized via amidation reaction. The results of Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) show that the 2-bromoisobutyryl bromide were covalently attached to the surface of silica nanoparticles, and there were 370μmol initiator in every gram of SiO2-Br.2. Poly (glycidyl methacrylate) (PGMA) was grafted onto the surfaces of nano-silica (SiO2) via surface-initiated ATRP. The obtained SiO2-g-PGMA hybrid nanoparticles reacted with excess ethylenediamine, which made the chain of PGMA possess many amine groups. Then, amine group and silver nitrate became silver/amine complex compound. Last, the silver/amine complex compound was reduced by sodium borohydride deoxidate, leading to Ag/SiO2-g-PGMA nano composited particles. The results of X-ray photoelectron spectroscopy (XPS) spectra, X-ray Diffractometer (XRD) and transmission electron microscope (TEM) show that the resulted composited particles were zero-valent silver, whose sizes were only several nanometers, and they were uniformly dispersed.3. The hybrid nanoparticles of SiO2-g-PMMA-b-PGMA was synthesized via surface-initiated ATRP, and a kind of immobilized ligand was synthesized via the Michael addition reaction between methylacrylate (MA) and triethylenete tramine(TEEA) on the surfaces of nano silica organic/inorganic hybrid particles. The resulting immobilized ligands were utilized for the ATRP of methyl methacrylate (MMA). Kinetic curves show linear dependence of ln([M0]/[Mt]) on time, and molecular weights of the poly(methyl methacrylate) increases linearly with monomer conversion. The immobilized catalyst system was easily separated from the polymer by centrifugation. Moreover, the reclaimed catalyst system can be reused for the ATRP of MMA, and polymerization reaction was also controlable and living. This conquered the problem of remove the transition metal catalyst after the polymerization in the traditional ATRP.4. Poly (styrene) (PS) was grafted onto the surfaces of nano-silica (SiO2) via surface-initiated ATRP, and the modification of high density polyethylene (HDPE) with the hybrid nanoparticles of SiO2-g-PS was studied.The results of Fourier transform infrared spectra (FTIR), transmission electron microscope (TEM), scanning electron microscope (SEM), and mechanical property measurements show that the hybrid nanoparticles of SiO2-g-PS were more easily dispersed in the matrix than bare nano-SiO2. Consequently, the notched impact strength and tensile strength of HDPE/SiO2-g-PS composites are superior to the pure HDPE and the HDPE/SiO2 composites. With the help of compatilizer (SEBS), the hybrid nanoparticles of SiO2-g-PS dispersed in the matrix more uniformly, and the mechanical properties of composites were improved greatly. While the content of the hybrid nanoparticles of SiO2-g-PS is 5%, the notched impact strength of HDPE/SEBS/SiO2-g-PS composites is 1.58 times more than the pure HDPE. Meantime, the tensile strength can also reach 26.31 MPa.