Maximizing polymer livingness in nitroxide-mediated miniemulsion polymerizations

Recent efforts to adapt nitroxide-mediated living radical polymerization chemistry to colloidal systems have shown considerable progress when miniemulsions are used. Miniemulsion SFRP in fact can yield higher conversions (>99%) and faster reaction rates than bulk SFRP. Much of the advantage of operating in miniemulsion arises from the inherent advantages of having a two phase system, in which the aqueous phase can be employed as a medium to introduce rate enhancing additives such as ascorbic acid to the reaction loci with a high degree of control. Additives such as ascorbic acid act by consuming excess nitroxide, and therefore directly influence the rate. Results on the effect of ascorbic addition on rate, molecular weight and livingness are presented. We have also begun to address the issue of high operating temperatures in TEMPO-mediated SFRP (∼120-135 °C) that require a pressurized reactor. We have run experiments using TEMPO at 100 °C with slowly decomposing initiator added to maintain an appropriate free nitroxide concentration. Reasonable reaction rates are obtained, albeit with higher polydispersities (∼1.6). Challenges and opportunities related to lower temperature operation are discussed.