Controlled Free-Radical Polymerization of n-Butyl Acrylate by Reversible Addition-Fragmentation Chain Transfer (RAFT) in the Presence of tert-Butyl dithiobenzoate. A Kinetic Studyстатья
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Аннотация: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 (Mn) 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.