Controlled free radical polymerization of styrene in the presence of nitroxide radicals I. Thermal initiation

摘要

The thermal autopolymerization of styrene in the presence of Tempo (2, 2, 6, 6-tetramethyl-1-piperidinyloxy free radical) was studied at 120 deg C. The use of Tempo allows to achieve the "living character" of bulk polymerization of styrene without any initiator described by a linearly increase of molecular weight in number with conversion and polydispersity close to 1.4. However, this study demonstrated that, at the end of bulk polymerizations of styrene in the presence of Tempo, the concentration of macromolecular chains is higher than the initial Tempo concentration (1/3) which is confirmed by the use of labelled Tempo by a trimethylsilyl group. The main consequence is that all macromolecular chains are not controlled by nitroxide radicals. Besides, the presence of Tempo during the thermal autopolymerization of styrene has an influence on the rate of the radicals formation generated by the Deals-Alder reaction: a transfer reaction of Tempo to the dimer of styrene is confirmed through kinetic studies and the rate of radicals formation is proportional to the Tempo concentration.