Kinetic studies on activation processes for organotellurium- And organostibine-mediated living radical polymerizations

The pseudo-first-order activation rate constant k_act was determined as a function of the propagating radical concentration for Organotellurium and organostibine-mediated living radical polymerizations (TERP and SBRP, respectively), showing that degenerative (exchange) transfer (DT) is the main activation process for these polymerizations. The exchange constant C_ex for TERP largely depended on monomers. For styrene, C _ex was about twice larger in SBRP than in TERP, explaining why the former exhibits better polydispersity controllability. The C_ex values for the poly(methyl methacrylate) (PMMA) radical to polystyrene-TeMe and PMMA-TeMe were similar. This is in sharp contrast to the previous observation that the C_ex for the same radical to PMMA-dithioacetate is about 50 times larger than to polystyrene-dithioacetate, where DT occurs via two steps mediated by the intermediate. This indicates that the DT in TERP occurs via a single step without forming a kinetically important intermediate.