The importance of exchange reactions in controlled/living radical polymerization in the presence of alkoxyamines and transition metals

The role of exchange reactions in controlled/living radical polymerizations is analyzed. Styrene polymerization in the presence TEMPO and atom transfer radical polymerization (ATRP) catalyzed by transition metals (Cu(II)X(2)/2Bipy complex) are compared. ATRP proceeds approximately one order of magnitude faster than TEMPO-moderated polymerization due to a higher stationary concentration of radicals and an equilibrium more shifted to the side of radicals. ATRP can provide better defined polymers with polydispersities down to M(w)/M(n) approximate to 1.05. This fact can be ascribed to a faster deactivation process and a smaller contribution of side reactions. The polydispersities in both systems are defined by the relative rates of the deactivation and propagation processes. The rate constant of deactivation of growing polystyryl radicals by TEMPO is in the range of k(d) approximate to 10(8) mol(-1). L . s(-1), which is substantially higher than the previously reported value.