Nitroxide-Mediated Radical Dispersion Polymerization of Styrene in Supercritical Carbon Dioxide Using a Poly(dimethylsiloxane-b-methyl methacrylate) Stabilizer

Nitroxide-mediated controlled/living dispersion polymerization of styrene in supercritical carbon dioxide (scCO 2 ) has been performed successfully to high conversion using N - tert - N -butyl- N -[1-diethylphosphono-(2,2-dimethylpropyl)] nitroxide (SG1) and a poly(dimethylsiloxane- b -methyl methacrylate) stabilizer at 110 °C. The molecular weight distributions were narrow ( M w / M n = 1.12−1.43), and the number-average molecular weight ( M n ) values agreed well with theory. A large excess of free SG1 was required to obtain satisfactory control in the dispersion polymerization, possibly due to SG1 partitioning. The critical degree of polymerization at which the polymer precipitates ( J crit ) was determined as 28 by visual observation using a novel approach. Polymerizations conducted in solution (toluene) proceeded at a similar rate (∼20% faster) to those in scCO 2 . The number of chains increased with conversion in both dispersion and solution, with the greater increase being observed in the dispersion system.