Nanoparticles Modified Via Surface RAFT Polymerization And Their Application

In this thesis, the RAFT agent, benzyl 9H-carbazole-9-carbodithioate (BCBD), was immobilized on the surfaces of two kinds of nanoparticles, SiO2 and cross-linked copolymer of styrene and 4-vinylbenzyl chloride synthesized, respectively. The surface RAFT polymerization of 4-vinylpyridine (4VP) was carried out on these nanoparticles to produce P4VP brushes on their surfaces. Several kinds of core-shell organic/inorganic hybrid nanomaterials were obtained. The results were shown as follows.(1) System 1: SiO2-supported organic/inorganic hybrid noble metal nanomaterials via surface RAFT polymerization. In this method, the synthesized SiO2 nanoparticles were first surface-modified by 4-(chloromethyl)phenyltrimethoxysilane coupling agent. Subsequently, the silica supported benzyl 9H-carbazole-9-carbodithioate (SiO2-BCBD) was synthesized as a solid supported RAFT agent by the reaction between the introduced benzyl chloride groups and carbazole as well as carbon sulfide. RAFT polymerizations of 4VP were then conducted from the nanoparticles surface to produce a well-defined and covalently tethered P4VP shell (SiO2-g-P4VP). By surface activation with Au3+ or Ag+ solution and then reduction by sodium borohydride (NaBH4), the out shell layer of core-shell SiO2-g-P4VP nanoparticles embedded with noble metal Au or Ag nanoparticles were obtained. The effect of polymerization time on the P4VP shell thickness was investigated, and it was found that the shell thickness could be controlled by the surface RAFT polymerization time. Some conventional characterization methods such as FT-IR, UV and TGA were used to confirm the successful synthesis of the SiO2-BCBD. The resultant SiO2-g-P4VP/metal nanoparticles were confirmed by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM).(2) System 2: Synthesis and application of polymer nanospheres with Pd/P4VP shells via surface RAFT polymerization. A RAFT agent with carbazole as Z-group was immobilized on the surfaces of the cross-linked poly (4-vinylbenzyl chloride-co-styrene) (PVBCS) nanospheres with a diameter of about 70 nm, which were obtained by emulsion copolymerization of 4-vinylbenzyl chloride and styrene in the presence of divinyl benzene, by the reaction between the benzyl chloride groups in the PVBCS and carbazole as well as carbon sulfide. Then surface RAFT polymerization of 4VP was used to modify the nanospheres to produce a well-defined and covalently tethered P4VP shell. By surface activation in a PdCl2 solution and then reduction by hydrazine hydrate (N2H4·H2O), the P4VP composite shells containing densely palladium metal nanoparticles were obtained. The effect of polymerization time on the P4VP shell thickness was investigated, and it was found that the shell thickness could be controlled by the surface RAFT polymerization time and therefore controlled the content of Pd nanoparticles in the polymer nanospheres. The chemical composition of the nanosphere surfaces at various stages of the surface modification was characterized by X-ray photoelectron spectroscopy (XPS). Transmission electron microscopy (TEM) was used to characterize the morphology of the hybrid nanospheres. The Pd/P4VP shell nanospheres were also applied to the catalytic reaction and proved to be efficient and reusable for the Heck reaction.