| Emulsion polymerization is one of the most widely used industrial processes for the synthesis of polymers by free radical polymerization. The prospect of performing living-radical polymerizations under emulsion conditions has been long awaited since it will allow the production of living polymers in an environmentally friendly and industrially compatible process. The extension of living-radical polymerization to emulsion has been met with a lot of problems. It is very difficult to maintain stable emulsions, ultimately leading to reactions that result in emulsion failure (latex instability, phase separation, and the formation of large particles).{09}The following thesis outlines attempts at performing stable free radical polymerization (SFRP) under emulsion conditions. Initial work was performed under ab initio SFRP emulsion conditions in which various factors were altered in attempts to obtain colloidally stable latexes. Although the polymers produced from these emulsions were living, the reactions consistently resulted in emulsion failure, producing latexes that phase separated into a foamy layer on top of a milky layer, or an emulsion containing large particles that settled to the bottom of the reaction mixture after the emulsion was left to stand for a few minutes. The failures resulting from this work led to the development of the nanoprecipitation emulsion process, in which an acetone solution of a low molecular weight TEMPO-terminated polystyrene was precipitated into an aqueous solution of poly(vinyl alcohol) to enable the formation of emulsion particles which were swollen with monomer and subsequently polymerized. The polymerizations behave in a living manner and produce colloidally stable emulsion latexes. The nanoprecipitation technique was successfully extended to the reversible-addition fragmentation chain transfer (RAFT) polymerization process to demonstrate the generality of this process. |
