Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Initiators with functionality bigger than one can be used in free radical polymerization (FRP) to increase the polymerization rate without decreasing the molecular weight of the polymer. The use of bifunctional initiators to produce linear polymers (like polystyrene and Poly(methyl methacrylate) (PMMA)) can be found in the literature; however, their application to produce branched polymers is rarer. This work reports the effect of the bifunctional initiator Luperox 531 (1.4-bi(t-butyl-carboperoxide) cyclehexane) on the FRP of vinyl acetate, which produces branched polymers. The monofunctional initiator Luperox TBEC (tert-butylperoxide-2-etyhexil carbonate) is also used as base of comparison. Polymerizations in ampoules have been performed in different temperatures and initiator concentrations. Results were compared to those obtained from the styrene polymerization, which produces linear chains. It can be concluded that the effect of bifunctional initiators on FRP depends strongly on the kinetic mechanism, kind of monomer, and operating conditions adopted. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013127317111716Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)