SiO₂ Nanoparticles Modified Via Surface-Initiated Living Radical Polymerization

In this thesis, two methods, namely, surface-initiated atom transfer radical polymerization using activators generated by electron transfer (AGET ATRP) mediated by iron catalyst and reversible addition-fragmentation chain-transfer (RAFT) polymerization, were used to synthesize well-defined organic/inorganic hybrid nanoparticles. The works can be summarized as follows:(1) System 1:Air-tolerantly surface-initiated AGET ATRP mediated by iron catalyst from silica nanoparticles (SiO2 NPs). SiO2 NPs with an average diameter of 78 nm were first prepared by St?ber method. ATRP initiators were immobilized on the surfaces of the SiO2 through the reaction ofα-bromoisobutyryl bromide and amino-functionalized SiO2, which were obtained by modifying with 3-aminopropyl triethoxysilane. Iron(III)-mediated surface AGET ATRP was then successfully carried out on the SiO2 using FeCl3·6H2O as the catalyst, PPh3 as the ligand, and ascorbic acid (VC) as the reducing agent, N,N-dimethylformamide (DMF) as the solvent in the presence of a limited amount air. The kinetics of the surface-initiated AGET ATRP of methyl methacrylate (MMA) from the SiO2 was studied in detail. Well-defined PMMA chains were grown from the SiO2 surfaces to yield hybrids composed of a SiO2 core and a densely grafted outer PMMA layer. Block copolymerization of linear and cross-linked P(PEGMA) from the macro-initiator (SiO2@PMMA) by surface-initiated AGET ATRP were proceed. The chemical composition of the nanocomposites was characterized by FT-IR spectroscopy, X-ray photoelectron spectroscopy (XPS) and 1H nuclear magnetic resonance (1H NMR) spectroscopy. Thermogravimetric analysis (TGA) was used to estimate the content of the grafted organic compound, and transmission electron micrographs (TEM) was used to observe the core-shell structure of the hybrid nanoparticles.(2) System 2:Triple functions of magnetic, thermoresponsive and fluorescent hybrid nanoparticles (NPs) were prepared via surface-initiated RAFT polymerization. In this method, the prepared Fe3O4 NPs, which is synthesized by conventional homogeneous precipitation method, were coated with SiO2 by the modified St?ber process. Subsequently, the magnetic silica NPs (Fe3O4@SiO2) were surface-modified by trichloro (4-chloromethyl phenyl) silane to obtain the chloromethylphenyl functionalized silica (Fe3O4@SiO2-Cl). Then, the Fe3O4@SiO2 supported benzyl 9H-carbazole-9-carbodithioate (Fe3O4@SiO2-BCBD) was synthesized as a solid supported RAFT agent by the reaction between the introduced benzyl chloride groups of Fe3O4@SiO2-Cl and carbazole as well as carbon sulfide. Finally, surface-initiated RAFT polymerizations of NIPAM were then conducted from the Fe3O4@SiO2-BCBD NPs surfaces to produce a well-defined and covalently tethered PNIPAM shell (Fe3O4@SiO2@PNIPAM). Some conventional characterization methods such as FT-IR, UV, TGA, TEM and EDS were used to confirm the successful synthesis of the Fe3O4@SiO2-BCBD and Fe3O4@SiO2@PNIPAM NPs. The existance of Fe3O4 in every sample was identified by vibrating-sample magnetometer (VSM) and X-ray diffraction (XRD). The stimuli-responsivity of Fe3O4@SiO2@PNIPAM NPs was confirmed by DLS, fluorescence spectrometer and external magnetic field.(3) System 3:The synthsis of magnetic and fluorescent organic/inorganic hybrid nanoparticles by RAFT polymerization in soap-free emulsion. In this method, the prepared hybrid RAFT agent, Fe3O4@SiO2-BCBD NPs in the system 2 were applied in a soap-free emulsion polymerization system containing of monomer (styene), water-soluble initiator (KPS) and deionized water. The organic/inorganic hybrid nanoparticles with covalently tethered PSt chains were produced with the"free"PSt particles at the same time. The retained RAFT agent on the surface of Fe3O4@SiO2@PSt was proved via the fluorescence test. The successful synthesis of the Fe3O4@SiO2@PSt NPs was confirmed by FT-IR, TGA and TEM.