| Nitroxide-mediated miniemulsion polymerization (NMMP) is one of several new “living” free radical polymerization processes that are capable of synthesizing polymers with controlled molecular weights and narrow molecular weight distributions, which can be pieced together to construct larger macromolecules. However, our ability to understand of the mechanisms involved NMMP is hindered by complex interactions between aqueous and organic-phase reactions.; To better understand the chemical conditions that exist in styrene NMMP, experimental studies were performed to measure the partition coefficients of commonly used nitroxides between styrene and water at temperatures between 25°C and 135°C, and to examine the influence of miniemulsion polymerization ingredients (e.g., hexadecane, surfactant and polystyrene) on the partitioning behaviour of nitroxides. Additionally, experiments were performed to measure the solubility of styrene in water at temperatures between 25°C and 35°C.; Using the results from our experimental studies and what is currently known about bulk styrene NMP, mathematical models were constructed to predict the behaviour of styrene NMMP systems initiated by alkoxyamines and potassium persulfate. Our models were employed to study the diffusional behaviour of nitroxides, the influence of nitroxide partitioning on NMMP kinetics, the effects of nitroxide-consuming side reactions on polymerization kinetics, the influence of aqueous-phase kinetics on the overall polymerization kinetics and possible ways to improve process performance. Additionally, our models were used to make quantitative estimates of the degree of polymer livingness, the aqueous- and organic-phase concentrations of nitroxide, the population of living and dead polymer chains, the relative importance of various polymer forming and radical termination reactions, and the MWDs of the individual polymer chains—quantities that have yet to be measured experimentally. |
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