How phase transfer increases the number of kinetic regimes from three to seven in nitroxide mediated polymerization of n-butyl acrylate in aqueous miniemulsion

One of the challenges in reversible deactivation radical polymerization (RDRP) in miniemulsion is identifying the optimal average particle size (dp), offering both high reaction rates and excellent control over chain length, branching level and functionality. In this work, a deterministic multi-dimensional Smith-Ewart model is combined with a method of moments model for nitroxide (N-(2-methyl-2-propyl)-N-(1-diethylphosphono-2,2dimethylpropyl)-N-oxyl; SG1) mediated polymerization (NMP) of n-butyl acrylate in miniemulsion. This model accounts for reaction and phase transfer, to showcase for the first time seven instead of three kinetic regimes in a broad dp range from 5 to 300 nm. The reliability of the model prediction is high because of (i) successful model validation under miniemulsion conditions at 385 K; (ii) unique consideration of & beta;-scission, allowing realistic prediction of the livingness; (iii) a validated temperature dependent SG1 partitioning coefficient; and (iv) many kinetic model parameters sourced from independent experimental validation under bulk/solution conditions. Pseudo-bulk kinetics (kinetic regime 1) and a dominance of the segregation effect (kinetic regime 2) are predicted at the highest dp. For decreasing dp, a novel regime 3 emerges in which exit of NMP initiator radicals is dominant. For even lower dp, dominance of free SG1 exit (kinetic regime 4), then dominance of the confined space effect first for NMP initiator radicals (kinetic regime 5), then the same but for free SG1 (kinetic regime 6), and rapid exit-entry dynamics with negligible termination (kinetic regime 7) are obtained. This work demonstrates that advanced population balance models for sustainable multiphase reactive processes can bridge experiment and simulation for improved functional material design.

Automated summary

One challenge in reversible deactivation radical polymerization in miniemulsion is finding the optimal particle size that allows for high reaction rates and control over chain length, branching, and functionality. In this study, a multi-dimensional Smith-Ewart model is combined with a method of moments model to investigate the NMP of n-butyl acrylate in miniemulsion. The model accounts for reaction and phase transfer and reveals seven kinetic regimes across a wide range of particle sizes. This work demonstrates the potential of advanced population balance models in bridging experiment and simulation for improved material design.