The present disclosure relates generally to a system having a reactor system with a polymerization reactor and a feed system fluidly coupled to a feed inlet of the reactor. The feed system supplies components to the reactor via the feed inlet, and the reactor has a flow path that continuously conveys the components through the reactor and subjects the components to polymerization conditions to produce a polymer. The system also has an analysis system coupled to the reactor for online monitoring of a particle size of the polymer. Further, the system includes a control system, coupled to the analysis and feed systems, that receives a signal from the analysis system indicative of the monitored particle size of the polymer and adjusts an operating parameter of the feed system to control a flow rate of at least one of the components to the reactor based at least on the signal.