Automatic Control of Polymer Molecular Weight during Free Radical Polymerization

A model-free, fully automatic feedback molecular weight controller was developed, which uses Automatic Continuous Online Monitoring Polymerizations (ACOMP) data. ACOMP provides continuous real-time monomer and polymer concentration, weight average molecular weight and intrinsic viscosity. The model-free controller uses two proportionality constants for monomer concentration and molecular weight control; i. alpha, monomer consumption rate constant and ii. p, monomer concentration proportional to weight average kinetic chain length. The controller has been successful for molecular weight control of linear chain growth free radical polymerizations. Using the ACOMP measurements, the instantaneous weight average molecular weight can be computed and folded into a chromatography-free molecular weight distribution (MWD). Hence, the evolution of the MWD can be monitored in real time and actively controlled. Multimodal distributions were achieved through the control of monomer and chain transfer agent concentration. Chain transfer agent is an optimal control for molecular weight because it affects chain length but not reaction kinetics. Furthermore, the APMT/PolyRMC controller has successfully controlled co-monomer composition and molecular weight by computing comonomer conversion kinetics and instantaneous comonomer fraction.