This paper presents an experimental study on the polymerization of droplets of methyl methacrylate (MMA) in quiescent state using microreactors. The reaction kinetics was monitored by Raman spectroscopy, while the images of MMA droplets image were captured by CCD (charge-coupled device) camera within a microcapillary. Different experimental recipes were proposed with commercial initiators in order to compare the system performance with two types of initiators: monofunctional and bifunctional peroxides. It is shown in this paper that the Raman technique is able to monitor the reaction kinetics at different conditions. For the first time in the open literature it was possible to identify the evolution of the monomer droplets during polymerization to high conversions ( > 90%) in quiescent state. In addition, it was possible to identify three different stages during the polymerization reactions of MMA. Finally, it is shown that the dispersities ((M) over bar (w) /(M) over bar (n)) obtained with the bifunctional initiator were lower than 2, while the dispersities obtained with the monolunctional initiator were greater than 2. (C) 2015 Elsevier Ltd. All rights reserved.