Modeling of atom transfer radical polymerization with bifunctional initiators: Diffusion effects and case studies

A mathematical model for atom transfer radical polymerization (ATRP) with bifunctional initiators was developed. The model was validated with three case studies in bulk and solution polymerization. We used only polymer yield data to estimate some of the model parameters, while others were obtained from the literature. The model fits the polymer yield data and also predicts weight-average molecular weights and polydispersities very well. The free volume theory was also incorporated to the model to study the effect of diffusion-controlled reactions. The adjustable parameters in the free volume theory for the termination, propagation, activation, and deactivation reactions were varied to show the effect on monomer conversion, polymer chain length, and polydispersity. The model shows that diffusion-limited termination reactions produce polymer with smaller polydispersities, while diffusion-limited propagation reactions have the opposite effect. Both models, considering and neglecting diffusion effects on the kinetic rate constants, were compared with experimental data. Even though the model predictions for monomer conversion, number-average molecular weight, and polydispersity are good in both cases, the simulations indicate that diffusion-controlled reactions can be ignored for the cases studied in the three case studies described in this paper.