Reactive Molecular Simulation and Microscopic Origins in the Reaction Kinetics of Binary Polymerization

The kinetics behavior of binary polymerization is studied by using reactive molecular dynamics simulation, and the polymerization reaction is represented by model systems consisting of two types of reactive monomers. The presence of the second reactive compound not only shifts the energy landscape but also alters the microscopic structure compared with the single-component system. Four model binary polymerizations are focused in the study including mixed polymerization, copolymerization, and grafting polymerization. The reaction kinetics of binary polymerization is dependent on reaction mechanisms and molecular properties of monomers. The intermolecular interactions and monomer sizes are two key factors influencing the microscopic structure to regulate the polymerization kinetics and properties of polymer products yielded, such as chain length distributions and chain sequences. The effect of binary polymerization is assessed by the hybrid function, which quantifies the deviation of binary polymerization from single mechanism polymerization. A microscopic expression of the hybrid function is derived based on the general collision reaction model and reactive algorithm in molecular dynamics (MD) simulation, in which both the reaction energy barrier and intermolecular interaction play pivotal roles. For binary polymerization considered in this study, the microscopic hybrid function is capable of modeling the reaction rates of binary polymerization at the molecular level compared with simulation data. The method is extended to model real binary polymerization of RAFT/ROP system, and the agreement between the theoretical model and experimental data shows the feasibility of describing the kinetics of binary polymerization based on the calculation of the hybrid function and homopolymerization. It allows us to adopt the hybrid function to extrapolate the kinetics of binary polymerization from homopolymerization using the critical physical quantities such as reaction energy barrier and statistically averaged intermolecular potential, both of which can be evaluated by first-principles chemical computations.