Millireactors offer the same advantages of microreactors, which are high surface to volume ratios and low Reynolds numbers (laminar flow). Polymerization reactions concerning high heat quantities and so it is an excellent example of medium that can be used in microreactors. The Syrris ASIA millireactor, 4.0 mL volume, was employed for the polymerization of styrene in toluene, performed at 100 degrees C and 115 degrees C. The objective is to produce polystyrene with the view of making the production more efficient. Different reagent quantities and residence times were used. Monomer conversions reached 67%, while number average molecular weight varied from 6000 to 50,000 g/mol. No plugging occurred, allowing more aggressive applications. The mass of the polymer product formed per volume of the reactor and time is about 0.1 kg/m(3)/s, which is higher than the values of the batch reactor (0.019 kg/m(3)/s) and of the tubular reactor (0.029 kg/m(3)/s). The fluid dynamic was evaluated as well by assuming reactor models. The PFR and the dispersion models were used to simulate the outputs, and gave a good forecast except for higher monomer contents, with larger polydispersities. To understand the microfluidic, the polymerization kinetic was also studied, using the full molecular weight distribution. (C) 2015 Elsevier B.V. All rights reserved.