First nitroxide-mediated free radical dispersion polymerizations of styrene in supercritical carbon dioxide

Controlled/living character has been demonstrated for the first time in nitroxide-mediated free radical dispersion polymerizations in supercritical carbon dioxide. Styrene was polymerized in the presence of N-tert-butyl-N-(1-diethylphosphono-2,2-dimethylpropyl) nitroxide (SG1) at 110 °C. Stabilization was achieved using the inistab concept (initiator+stabilizer), employing a poly(dimethylsiloxane) (PDMS) based azo initiator as well as a polymeric alkoxyamine macroinitiator with the expected structure SG1-polystyrene-PDMS-polystyrene-SG1. In the presence of sufficient amounts of the inistab, the polymerizations proceeded to high conversion to yield the polymeric product as a powder. Control was indicated by the number-average molecular weights increasing linearly with conversion in reasonable agreement with the theoretical values. Although the molecular weight distributions were broad in many cases, chain extensions in bulk and solution using styrene indicated high degrees of 'living' character.