Controlled free-radical polymerization of n-butyl acrylate by reversible addition-fragmentation chain transfer in the presence of tert-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 90degreesC. The polymerizations exhibited the expected features of controlled systems. In particular, the linear increase in number-average molar mass (M.) 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 90degreesC 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.