MECHANISM OF LIVING RADICAL POLYMERIZATION MEDIATED BY STABLE NITROXYL RADICALS

It is shown that in order for the ''living'' radical polymerization me diated by stable nitroxyl radical (SNR) to proceed successfully, a con stant supply of initiating radicals (by, e.g., thermal initiation) to make up for the loss of polymer radicals due to irreversible bimolecul ar termination is essential in addition to the frequent reversible com bination of polymer radical with SNR. The stationary rate of SNR-media ted polymerization is totally independent of the SNR concentration, be ing equal to the polymerization rate of the SNR-free system. Experimen tal evidence is presented showing that in the ''living'' polymerizatio n of styrene, both of these requirements are met in fact.