Mechanism of controlled/''living'' radical polymerization of styrene in the presence of nitroxyl radicals. Kinetics and simulations

The polymerization of styrene in the presence of a stable radical, TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy), has been simulated using a Predici simulations package. On the basis of the experimental data, a kinetic model for the TEMPO-mediated polymerization of styrene is proposed. In order to simulate the experimental data properly, it was necessary to include thermal self-initiation, transfer, and irreversible decomposition of intermediate alkoxyamines in addition to the reversible cleavage of the TEMPO-polymeric radical adduct. This model, combined with the values of the rate constants of propagation (k(p)), termination (k(t)), transfer (k(trm)), and alkoxyamines decomposition (k(decomp)), was then employed to estimate the kinetic and thermodynamic parameters for the exchange between dormant and active species. The equilibrium constant, K, was estimated to be approximately 10(-11) mol . L(-1) the deactivation rate constant, k(d) = 8 x 10(7) mol(-1). L . s(-1), and the activation rate constant, k(a) = 8 x 10(-4) s(-1), for bulk styrene polymerization at 120 degrees C.