Effects of the oil–water interface on network formation in nanogel synthesis using nitroxide-mediated radical copolymerization of styrene/divinylbenzene in miniemulsion

Nitroxide-mediated radical copolymerization of styrene (99 mol%)/divinylbenzene (1 mol%) employing the nitroxide 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO) in aqueous miniemulsion using sodium dodecylbenzenesulfonate as surfactant has been carried out at 125 °C. At a given styrene conversion, the degree of crosslinking increases with decreasing polystyrene–TEMPO macroinitiator concentration in excess of what is predicted based on the increase in primary chain length assuming an ideal controlled/living process. This discrepancy is mainly a result of the oil–water interface effect on the deactivation reaction between propagating radicals and TEMPO. This interface effect causes a marked increase in primary chain length, and therefore an accompanying increase in the number of crosslinks per primary chain. Polymerizations in the presence of free TEMPO minimizes the interface effect, and one then obtains molecular weight distributions and well-defined networks conducive with a controlled/living process.