Nitroxide-mediated radical polymerization (NMRP), in a continuous microtube reactor of 900 pm inner diameter, of styrene and n-butyl acrylate at high temperature has been performed. The influence of the microsystem reactor on the control of the polymerization reaction was investigated and compared to a conventional labscale batch reactor. The main advantage of this microsystern is its ability to handle highly exothermic chemical reactions because of its high surface to volume ratio and the possibility to carry out the polymerization process in homogeneous conditions due to its small characteristic length. The discrepancy between microtube and batch reactors increases as the exothermicity of the monomer increases. In almost all experiments, the microtube reactor gives smallest polydispersity indices. Thus, the use of microstructured reactors can significantly improve the control of the polymerization. (c) 2007 Elsevier Ltd. All rights reserved.