Synthesis of Microgels with Minimal Final Concentration of Initiator

Microgels are functional polymers with diverse applications synthesized by free radical polymerization using an initiator, monomers, and cross-linker as reactants. While monomers and cross-linker are incorporated into the microgel during the synthesis, initiator is left in the reactor due to its slow decomposition rate. The removal of unreacted initiator is a challenging and time-consuming post-synthesis procedure. Therefore, we use model-based dynamic optimization to determine synthesis procedures that reduce in the final concentration of unreacted initiator. The dynamic optimization requires a mechanistic model of the microgel synthesis, that needs to consider the inhibition of residual oxygen in the reactor at the beginning of the synthesis. Residual oxygen might inhibit the initiation of the synthesis when initiator concentrations are sufficiently low. We extend our existing model with the effect of an initial oxygen inhibition. We then use dynamic optimization to minimize the initial initiator concentration, while maintaining process and quality constraints. The considered product quality constraint is the hydrodynamic radius of the microgel, which must not change by more than 5 %. The determined synthesis procedure shows a 76 % reduction in the final concentration of unreacted initiator in comparison to the reference case, while maintaining the reference microgel hydrodynamic radius. The synthesis time, however, is 48 % longer than the synthesis time of the reference case. Hence, there is a trade-off between the final initiator concentration and the duration of the microgel synthesis demonstrating the value of dynamic optimization for the determination of optimal synthesis conditions valuable.