Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Free radical polymerization is a very robust route to produce polymers, however, it does not promote a control on the microstructure of the polymer: usually polymers with wide molecular weight distribution and polydispersity (PDI) greater than 1.5 are obtained. Ionic polymerization can be used to produce polymers with low PDI, however, this kind of route needs to be held with a high degree of purity. Living free radical polymerization (LFRP) is a promising technique to produce controlled polymers. In the literature, monofunctional conventional initiators have been used in LFRP process. In this study, the use of a cyclic trifunctional peroxide on controlled nitroxide mediated radical polymerization was investigated. The initiator used was Trigonox 301 (3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonane41% solution in isoparaffinic hydrocarbons) and TEMPO (2,2,6,6-tetramethyl-1-piperidin-1-oxyl) was used as controller agent. The results obtained show that it is possible to produce controlled polymers at certain operating conditions, when Trigonox 301 is used. It could be observed that the concentration of initiator and the ratio [TEMPO]/[Trigonox 301] have a huge effect on the polymer properties. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012124539003904Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)