Modeling and Prediction of Microgel Synthesis: Conversion, Growth and Structure

Microgels are cross-linked polymer networks in size of 10 - 1000 nm. In this thesis, three predictive models for the synthesis of poly(N-Vinylcaprolactam)-based microgels by precipitation polymerization are developed. The three models address the three characteristic properties of microgel synthesis - conversion, microgel growth and internal structure.

The first model is a reduced two-phase model, which is used for the investigation of the reaction progress and thus conversion in the microgel synthesis. The integration of parameter values from quantum mechanical calculations as well as experimental investigations elucidates the copolymerization of the monomer N-Vinylcaprolactam with the cross-linker. Further, it provides insight into fundamentals of the reaction, such as the primary reaction locus.

The second model describes additionally microgel growth as well as their size distribution. Simulations show the importance of radical absorption and aggregation for the microgel growth. The uniform size distribution, which is typically obtained by precipitation polymerization, is thus the result of a short initial nucleation phase, which is followed by even growth of the formed microgels.

The third model is a hybrid Kinetic Monte Carlo model. It provides additionally a prediction of the internal microgel structure. Stochastic simulation predicts the discrete aggregation of microgels as well as the individual reactions within the microgels. This model provides the fundamentals for a detailed depiction of the polymer network of microgels.

The three models increase in the degree of detail. Therein, the models of higher fidelity benefit from the knowledge gained from the previous models. While the first and simplest model is best suited for the combination with experimental analysis and thus, model-based control and optimization, the third and most complex model is rather of predictive nature to complement experimental investigations. With step-by-step model development and incorporation of new approaches such as quantum mechanical calculations, the complexity of modeling the microgel synthesis is resolved.