Controlled Free-Radical Polymerization ofn-Butyl Acrylate by Reversible Addition−Fragmentation Chain Transfer in the Presence oftert-Butyl Dithiobenzoate. A Kinetic Study

The RAFT polymerization of n -butyl acrylate was studied in the presence of various concentrations of tert -butyl dithiobenzoate (t-BDB) as a chain transfer agent, and various concentrations of AIBN as an initiator at 60 and 90 °C. The polymerizations exhibited the expected features of controlled systems. In particular, the linear increase in number-average molar mass ( M n ) with monomer conversion, from very low conversion values, indicated a large apparent chain transfer constant to t-BDB. The kinetic study showed two typical characteristics already observed in RAFT polymerizations of various acrylates: the existence of an induction period and a strong rate retardation, both enhanced by the increase in t-BDB initial concentration. ESR spectroscopy was applied at 90 °C and revealed the existence of an unexpectedly large concentration of intermediate radicals. The system was examined and discussed considering either the possibility of cross-termination between a propagating macroradical and an intermediate one, with fast fragmentation of the intermediate radicals or the absence of cross-termination but slow fragmentation.