What are the challenges in controlling polymerization reactors?

Challenges: highly exothermic reactions with low thermal conductivity polymer, viscosity increases dramatically with conversion (affects mixing, heat transfer), molecular weight distribution depends on temperature history (requires tight control), multiple product grades requiring transitions, fouling on heat transfer surfaces, and runaway potential. Control strategies: monomer feed rate manipulation, jacket temperature control, reflux cooling, controlled initiator addition, and grade transition scheduling. Continuous processes use multiple zones; batch uses programmed temperature trajectories. Online monitoring (viscosity, Raman) enables quality control.