Mechanistic investigation of particle size effects in TEMPO mediated radical polymerization of styrene in aqueous miniemulsion

Particle size effects in the diameter range 70-200 nm in 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO)-mediated radical polymerization of styrene in aqueous miniemulsion at 125 degrees C using sodium dodecylbenzenesulfonate as surfactant have been studied. Extensive investigations, including modeling and simulations of the polymerization, indicate that a significant fraction of free TEMPO is unable to participate in deactivation reactions if the particles are sufficiently small. The results are in support of our previously proposed interface effect [Nakamura, T.; Zetterlund, P. B.; Okubo, M. Macromol. Rapid Commun. 2006, 27, 2014-2018], according to which some fraction of the free TEMPO is located/adsorbed at the interface, thus reducing the effective TEMPO concentration in the organic phase.