Synthesis Of Composite Nanomaterials Emulsion By Atom Transfer Radical Polymerization In Aqueous System

Atom transfer radical polymerization (ATRP) is a suitable method for the controllable molecular weight and structure of polymer. As one of the most effective methods, the surface initiated atom transfer radical polymerization (ATRP) is a choice for grafting the surface of nanoparticles with a shell of organic polymer. The composite nanomaterials combine the virtues of controlled/"living" polymerization with the merits of the inorganic nanoparticles and organic polymer.In this dissertation, the PSt latex with a narrow molecular weight distribution was synthesized successufully by surface-initiated atom transfer radical polymerization using water as medium in miniemusion. The polymerization process, mechanism and characteristic of atom transfer radical polymerization in aqueous system were discussed. The effects of surfactant type and structure of ligands on the control of reaction and latex stability were examined in detail. In addition, the effects of various parameters and conditions on polymerization in water system were investigated. The results indicated that the control of polymerization with miniemulsion system was better than the conventional emulsion system. The distribution of catalyzer in organic and aqueous phase had an important influence on the control of polymerization. The result showed that the reaction gave the best latex stability and the perfect control of molecular weight on the dosage of emulsifier (TW-80) 15.4%(g/g-St),aid emulsifier 3%, the amount of catalyst system (CuCl/dNbpy) 0.15(mol/mol-St), the temperature 70℃. The molecular weight increased linearly with the increase of conversion. The molecular weight of the sample obtained can be adjusted by ratio of [M]0/[I]0. The sample was characterized with GPC,FI-IR,TEM,SEM,DLSand TGA. The results showed that the polymer presented a lower polydispersities of about 1.32. The polystyrene latex particles were uniform spherical with a diameter of about 200 nm.On the based of above study, the grafted nano SiO2/PSt composite latex was prepared by'ATRP. First the nanoparticles were modified, then the initiator was grafted to the surface of nanoparticles. Finally the polystyrene shell was grafted from the initiating sites on the surface of nanoparticles. The results showed that silane coupling agent can react with -OH groups on the surface of SiO2 particles. The temperature of modification and grafting was 65℃and 70℃, and the percentage of loading and grafting was 21% and 12%, respectively. The grafted nano SiO2/PSt composite latex possessed conversion rate of 85% and grafting efficiency of 81%, under the condition of the ratio of SiO2-Cl and the monomer 0.06 and the reaction temperature 80℃. The polymer latex obtained had a narrow molecular weight distribution (Mw/Mn=1.34) with a perfect stability. By the analysis of TGA, the thermal decomposition temperature of nano SiO2/PSt elevated about 40℃higher than the decomposition temperature of polystyrene, which heat resistance has been further improved.