Mechanism and Kinetics of Organostibine-Mediated Living Radical Polymerization of Styrene

The polymerization of styrene with a polystyrene-dimethylstibanyl (PS-SbMe 2 ) adduct as a mediator and azobis(isobutyronitrile) (AIBN) as a conventional radical initiator was kinetically studied. PS-SbMe 2 had no detectable effect on the polymerization rate R p , which was virtually the same as that of the conventional (stibanyl-free) system. The pseudo-first-order activation rate constant k act was proportional to R p , meaning that degenerative (exchange) chain transfer is the only important activation mechanism, in the examined range of temperature (40–100 °C). The exchange rate constant k ex was sufficiently large at these temperatures, explaining why this polymerization can afford low-polydispersity polymers. The k ex was about twice as large as that for polystyrene-methyltellanyl (PS-TeMe). This rationalizes the better polydispersity controllability in the PS-SbMe 2 system than in the PS-TeMe system. The activation energy of k ex was 22.6 kJ mol −1 , which is smaller than that (27.8 kJ mol −1 ) for polystyrene-iodide (PS-I) and slightly larger than that (21.0 kJ mol −1 ) for polystyrene-dithioacetate (PS-SCSMe).