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 × 10 7 mol -1 ·L·s -1, and the activation rate constant, k a = 8 × 10 -4 s -1, for bulk styrene polymerization at 120 °C.