The effects of the reaction conditions and nature of the initiator were investigated in the Cp2Ti(III)Cl-catalyzed living radical polymerization of styrene initiated by benzoyl peroxide (BPO), tert-butyl peroxide (TBPO), tert-butyl peroxybenzoate (TBPOB), dicumyl peroxide (CPO), and tert-butylperoxy 2-ethylhexyl carbonate (TBPOEHC). The reversible termination of the growing chains with Cp2Ti(III))Cl affords a linear dependence of molecular weight on conversion over a wide range of temperatures (60-120 degrees C) with an optimum in polydispersity (M-w/M-n < 1.2) for St/BPO/ Cp2TiCl2/Zn = 100/1/3/6 at 60-90 degrees C. The similarity of the kinetic parameters from polymerizations initiated by peroxides with vastly different half-life times (t(1/2)(BPO, 90 degrees C) = 1h, t(1/2)(TBPO, 90 degrees C) = 543 h) and the minimum peroxide/Ti = 1/2 ratio required for a living process indicate that initiation occurs primarily by the redox reaction of the peroxide with Cp2Ti(III)Cl rather than peroxide thermal decomposition. This is consistent with one Ti equivalent consumed in the redox initiation and the second one utilized in the reversible termination of the growing chains. Qualitatively, based on the livingness of the process, these initiators ranked as BPO > TBPOB similar to TBPO > CPO > TBPOEHC. (c) 2005 Wiley Periodicals, Inc.