To evaluate the structural effect of nitroxides on the living free radical polymerization of styrene, substituted pyrrolidinyloxyls and an oxazolidinyloxyl were synthesized and employed as mediators at 110 °C.All the cyclic nitroxides, except oxazolidinyloxyl were found to control different extents the molecular weight (M n ) and polydispersity (M w /M n ) of the polystyrene samples obtained. Among the nitroxides synthesized, 2,2,3,3,5-pentamethyl-5-phenylpyrrolidinyloxyl and 2,3,3,5-tetramethyl-2,5-diphenylpyrrolidinyloxyl, are of particular interest because polystyrene samples with M n > 100000 and M w /M n < 1.5 were obtained whereas 2,2,6,6-tetramethylpiperidinyloxyl yielded polymers with considerably lower M n and slightly lower M w /M n under similar conditions. The polymerization in the presence of oxazolidinyloxyl radical was found to proceed almost without any influence of the nitroxide.The living free radical polymerization (LFRP) of styrene (St) mediated by 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO) has drawn much attention, because LFRP enables to control molecular weight and molecular weight distribution of the polymer by preservation of the activity of propagating radical through the reversible deactivation by TEMPO (7-7). Indeed, the propagating species rapidly reacts with TEMPO to form an alkoxyamine as dormant species that can regenerate the propagating radical and TEMPO upon thermally activated dissociation. The formation of the reversible bond from the propagating radical and TEMPO reduces the steady state concentration of the active radicals and leads to the diminution of the probability of uncontrolled bimolecular termination.
Overview of TEMPO Mediated PolymerizationRecently, it has been revealed that thermal initiation of St, bimolecular termination, chain transfer to the reactive dimer produced by thermal initiation of St, and degradation of the alkoxyamine into an unsaturated group at polymer chain end and a hydroxyamine occur concurrently in the LFRP system (5-8).Furthermore, the 'Corresponding author 200
