| The majority of the research presented in this thesis is focused on applying atom transfer radical polymerization (ATRP) to the aqueous dispersed system. ATRP is one of the most versatile living/controlled radical polymerization techniques that allow for the preparation of polymeric materials with well-defined molecular weights, compositions, functionalities and architectures.; A number of successful examples are given for the homo- and copolymerizations of methacrylates, acrylates and styrenes via direct ATRP. The influence of ligand, surfactant, initiator and other experimental conditions was explored in order to optimize the recipe and procedure. Conventional water-soluble thermo-initiators can also be used to trigger the reverse ATRP process. Stable latexes with particle diameters within 150–300 nm were formed. The influence of the concentrations of the catalyst, the surfactant and the initiator, as well as the temperature on the polymerization rate, molecular weight and particle size was investigated. The employment of ultrasonication in combination with a hydrophobe was also successful in achieving both controlled polymerization and stable latex. The direct ATRP most likely proceeds via a suspension process, whereas reverse ATRP displays more unique features. Due to the lack of high molecular weight polymer during the early polymerization stage, reverse ATRP in the aqueous dispersed system presumably has a different “nucleation” mechanism from that of a conventional emulsion polymerization. In addition, fast decomposition of the initiator prevents the continuous entry of radicals into the particles from the aqueous phase. As a result, the kinetics of the reverse ATRP is fundamentally different from a classical emulsion polymerization, and is controlled mainly by the atom transfer equilibrium.; The second part of the thesis concerns several structure-reactivity relationships in ATRP. The catalyst structures were investigated via UV spectroscopy. It revealed several equilibrium reactions between different copper species in solution, which depends on the solvent polarity, temperature, ligand to copper ratio, and the total copper concentration. The results also suggested that the original proposed ATRP mechanism was essentially correct except the nature of the counterions for both CuI and CuII species. A correlation between the redox potential and the apparent equilibrium constant of ATRP for methacrylate was observed. (Abstract shortened by UMI.)... |
