'Living' Free Radical Polymerizations: Role of Autopolymerization and Nitroxide Mobility

摘要

One of the most intriguing features of nitroxide mediated 'living' free radical polymerizations is the low polydispersities obtained for the polymeric products with values typically between 1.10 and 1.30.] One of the reasons for these exceptionally low polydispersities is the reduced occurrence of side reactions such as termination. This results in controlled molecular weights,2 chain ends,3 and polymeric architectures.4 Such a high degree of controlover macromolecular structure is surprising given that this is a radical polymerization which is conducted at 120-130°C for extended periods of time. In trying to account for these observed features a number of important questions arise: is autopolymerization occurring during these polymerizations and if so, what is the fate of the polymer chains initiated by the radicals produced by autopolymerization? Also how closely associated are the growing radical chain ends with the mediating nitroxide radicals, is a pseudo radical pair formed or are the nitroxide free radical free to diffuse into the polymerization mixture and hence migrate from chain end to chain end? To answer these questions we have examined in detail the role of autopolymerization and nitroxide mobility in living' free radical polymerizations.