Modeling the star-branched polymer coupling reaction in continuous reactors: Effects of the operating conditions on the molecular weight distribution

Star polymers, consisting of many arms connecting to a central core, represent a branched nanoscale material with compact structure and large surface area. Their synthesis is usually performed by making use of living polymers made by anionic polymerization as arms, and multifunctional compounds as linking agents. In general, polymer blends resulting from the star coupling process exhibit some polydispersity, which is influenced by (i) the polydispersity of the primary chains and (ii) the kinetics of the linking processes to the coupling agent. In the present contribution we develop a mathematical model for the description of the star coupling process in continuous reactors. The proposed model is based on the following statements: (i) the characterization of the MWD of the branched polymer species is accomplished by exploiting a probabilistic approach and (ii) the concentration of the single species is evaluated through implementation of mass balance equations, where the reactions describing the linking of the living polymers to the active branched unit are modelled with first and second order kinetics. The final goal is to predict the MWD shape when varying the operating conditions (i.e.: concentration of polymers and multifunctional agents in the feed flow and residence time)