Compartmentalization in Nitroxide-Mediated Radical Polymerization in Dispersed Systems

Modified Smith−Ewart equations were used to quantitatively investigate compartmentalization effects in nitroxide-mediated radical polymerization in dispersed systems. Calculations were carried out for the specific system 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO)/styrene at 125 °C with thermal initiation included in the model, and accounting for compartmentalization of both propagating radicals and nitroxide. For particles with diameter ( d ) less than approximately 60 nm, a reduction in particle size led to lower rate of polymerization, higher degree of livingness, and a higher number of activation−deactivation cycles experienced per chain to grow to a given degree of polymerization. These effects have their origin in the pseudo first-order deactivation rate coefficient increasing in proportion to d -3 with decreasing particle size. There were no significant effects of compartmentalization for particles with d > 110 nm. The results show that it is important to consider compartmentalization effects also on the deactivation reaction, and not only bimolecular termination.