Controlled radical polymerization of n-butyl acrylate by reverse iodine transfer polymerization (RITP) was achieved in ab initio emulsion polymerization to yield a stable and uncolored latex (particle diameter d(p)=106 nm). Hydrolysis of iodine, 12, was responsible for an upward deviation from the targeted molecular weight (M) over bar (n,targeted) 10400 g center dot mol(-1). The iodide concentration [I-] was followed by an iodide selective electrode and the amount of efficient iodine (33%) was successfully correlated with the experimental molecular weight (M) over bar (n,exp)=31000 g center dot mol(-1). Finally, a simplified mechanism of RITP in ab initio emulsion polymerization taking into account the iodine hydrolysis was proposed.