The authors developed within a project funded by the German government a micro reaction plant which allows to produce polymers out of up to 8 monomers by using the Suzuki coupling method. Micro reactors can have a positive influence on the quality of the polymer product. Especially the mixing quality of the monomers, the catalyst solution, and end capper solutions have a great influence on the molecular weight distribution. With micro reactors it is possible to have a very narrow distribution which is not achievable in typical batch processes. To monitor the product quality a new sensor was developed to measure online the product viscosity and with this the molecular weight of the polymer. (C) 2010 Elsevier B.V. All rights reserved.