Interplay between Reaction Kinetics and Particle Growth during Emulsion Polymerization Revealed by Stochastic Modeling

Most emulsion polymerization kinetic models rely on the 0–1, pseudobulk, or pseudosteady state assumptions and have difficulty in distinguishing particles formed by different nucleation mechanisms. Herein, a kinetic Monte Carlo algorithm is developed to simulate reactions and mass transfer phenomena during emulsion polymerization. This approach avoids these assumptions and explicitly tracks the nucleation mode, chemical composition, and size of each particle. Due to the compartmentalization effect and the dependence of mass transfer rates on particle size, the kinetic characteristics vary among particles. Larger particles remain reactive, grow, and accumulate dead chains, while smaller particles struggle to grow. The high initiation rate of primary radicals improves nucleation efficiency and controls molecular weight distribution. Simulation results show that increasing the contribution of homogeneous nucleation reduces the total number of particles and broadens the molecular weight distribution, which is driven by competition among homogeneous nucleation, aqueous-phase termination, and radical entry. Additionally, the growth rate of homogeneous-nucleated particles strongly depends on their nucleation time. These findings reveal the interaction between polymerization kinetics and particle growth, and offer novel insights into how the ratio of micellar to homogeneous nucleation affects particle size and molecular weight distribution.