Nitroxide-mediated radical polymerization of styrene in emulsion

The emulsion polymerizations of styrene in the presence of a variety of TEMPO derivatives were investigated. Among the TEMPO derivatives we studied, 4-acetoxy-2,2,6,6-tetramethylpiperidine-1-oxy (ATEMPO) was a suitable candidate for a living radical polymerization in emulsion, because it provided an optimized balance between hydrophilic and hydrophobic character. For the emulsion polymerization of styrene in the presence of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxy (HTEMPO), however, the slow initiation in aqueous phase due to the strong hydrophilic character of HTEMPO, hindered styrene polymerized in a living fashion. The emulsion polymerization of styrene in the presence of 4-benzoyloxy-2,2,6,6-tetramethyl-piperidine-1-oxy (BTEMPO) who was absolutely rich in organic phase, was uncontrolled and identical to conventional radical polymerization.