With the purpose of enhancing the reaction rate of nitroxide-mediated radical polymerization of styrene (NMRP) in presence of TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy), keeping the livingness of the system, the effect of a bi-functional initiator has been examined, a new approach. The monomer used was the styrene, the stable radical was TEMPO, the mono-functional initiators were BPO and Luperox TBEC, and the bi-functional initiator was Luperox L531. The polymerization reactions were carried out in ampoules at 125°C, according to the bi-molecular technique. The conversion was evaluated by a gravimetric method, and the molecular weight distribution and the polydispersity of the polymer were analyzed by SEC (Size-Exclusion Chromatography). The effects of the use of the bifunctional initiator and the mono-functional ones with different half-life times have been evaluated. It was demonstrated that by using the bi-functional initiator L531, the reaction rate was increased when comparing to the performance of the mono-functional initiatiors, under the conditions of the reaction. Georges, M.K., Veregin, R.P., Kasmaier, P.M., Hamer, G.K., (1993) Macromolecules, 26, p. 2987Veregin, R.P.N., Odell, P.G., Michalak, L.M., Georges, M.K., (1996) Macromolecules, 29, p. 3346Butté, A., Storti, G., Mobidelli, M., (1999) Chemical Engineering Science, 54, pp. 3225-3231Solomon, D.H., Rizzardo, E., Cacioli, P.U.S., (1986) Pat, 4, pp. 581-429Vilallobos, M.A., Hamielec, A.E., Wood, P.E., (1991) Journal of Applied Polymer Science, 42 (3), pp. 629-641Benbachir, M., Benjelloun, D., (2001) Polymer, 42, pp. 7727-7738Asteasuain, M., Brandolin, A., Sarmoria, C., (2004) Polymer, 45, pp. 321-335Penlidis, A., Gao, J., Dhib, R., (2000) Polymer Reaction Engineering, 8 (4), pp. 299-246Sanchez, J., Myers, T., Peroxides and Peroxide Compounds: Organic Peroxides (1996) Kirk-Othmer Encyclopedia of Chemical Technology, 18. , 4 th ed. WileyInitiators: Free Radical Peroxides, ibid, 13., 1996Fukuda, T., Goto, A., (1997) Macromolecules, 30, p. 4272Matyjaszewsky, K., Greszta, D., (1997) Journal of Polymer Science, Part A: Polymer Chemistry, 35, p. 1857