Predictive Control of Average Composition and Molecular Weight Distributions in Semibatch Free Radical Copolymerization Reactions

Control of copolymer composition and molecular weight distributions is important, since they partially govern material performance. This work uses a simple but robust approach to approximate predictive control of average composition and molecular weight during free radical copolymerization, based on detailed kinetics obtained by ACOMP (automatic continuous online monitoring of polymerization reactions). Using these kinetics and elementary computations as a guide, the trends in the composition and molecular weight drifts during synthesis can be approximately controlled by predetermined, constant reagent flows into the reactor (“semibatch” operation). Two comonomer systems were chosen: one comonomer pair with very different reactivity ratios, having a tendency to high composition drift, and the other onewithmuch closer reactivity ratios resulting in relatively constant composition during batch copolymerization. Each system had high downward molecular weight drift during synthesis, typical of free radical polymerization. Appropriate feed polices were found to control the composition andmolecular weight drift tendencies at will; i.e., it was possible to keep composition constant in the first case and to increase or decrease composition in the latter, while desired trends for the average molecular weight were also obtained. The approach allows practical, approximate composition and molecular weight control in free radical copolymerization with simple reactors and pumps and without computationally intensive requirements. The results can also be useful as anAnsatz for reaction trajectory prediction and, together with the onlinemonitoring signals, can be used for feedback controlled corrections to the reagent flows and other reaction conditions.