Criteria for Livingness and Control in Nitroxide-Mediated and Related Radical Polymerizations

摘要

In nitroxide mediated radical polymerizations large living and controlled polymer fractions at high conversions require equilibrium constants of the polymeric alkoxyamine dissociation-coupling cycle K =k_d/k_c that are smaller than A~(max) = k_p[I]_0/2ln(10)k_t. Perfect livingness is reached if K ≈ K~(max)/100. These conditions imply minimum monomer conversion times. Small polydispersity indices at moderate to large conversions result if k_dk_c is close to or above a limit k_dk_c~(perf) = 9(k_p/2ln(10))~3[M]_0~2/[I]_0k_t. The limits depend on the propagation and termination constants (k_p, k_t), that is, on the monomer, and on the initiator concentration [I]_0. Five cases with different time evolutions of conversion, livingness and molecular weight distribution are distinguished. They explain the course of reported polymerizations. Effects of initially present persistent radicals, self- and external initiation and reaction temperature are discussed. Further, the criteria are translated to apply also to atom transfer radical polymerizations.