Nitroxide‐mediated polymerizations of styrene in microemulsion have been carried out at 125 °C using the cationic surfactant tetradecyltrimethylammonium bromide and the nitroxides 2,2,6,6‐tetramethylpiperidinyl‐1‐oxy (TEMPO) and N‐tert‐butyl‐N‐[1‐diethylphosphono‐(2,2‐dimethylpropyl)] nitroxide (SG1). TEMPO‐mediated polymerizations were extremely slow, with large particles (dn = 39–129 nm) and broad molecular weight distributions (MWDs). The origin of the broad MWDs was likely significant alkoxyamine decomposition and differing diffusion rates of monomer and low MW alkoxyamines (and nitroxide) between monomer‐swollen micelles and polymer particles. SG1‐mediated polymerizations proceeded at higher rates, resulting in nanoparticles (dn = 21–37 nm) and lower $\overline M _{\rm w} /\overline M _{\rm n}$ than for TEMPO.magnified image

Nitroxide-mediated radical polymerizations (NMP) of styrene at 100 °C using the cationic emulsifier tetradecyltrimethylammonium bromide (TTAB) have been carried out employing 2,2′-azoisobutyronitrile (AIBN) and two nitroxides of different water solubilities. The polymerization rate was lower and the molecular weight distribution more narrow in microemulsion than bulk at low conversion. The results can be rationalized based on the lower initiator efficiency in microemulsion than bulk, presumably caused by the confined space effect (compartmentalization) on geminate termination of AIBN radicals, and possibly also the confined space effect causing an increase in deactivation rate. The extent of retardation relative to bulk was more severe for the less water-soluble 2,2,5-trimethyl-4-phenyl-3-azahexane-3-oxy (TIPNO) than the more water-soluble N-tert-butyl-N-[1-diethylphosphono-(2,2-dimethylpropyl)] nitroxide (SG1) as expected based on more extensive nitroxide exit occurring in the case of SG1 than TIPNO. The results illustrate how effects of heterogeneity can profoundly influence the course of NMP in dispersed systems.

Notes† Part CCCXLIII of the series "Studies on Suspension and Emulsion".