Kinetic Model of Free Radical Polymerization without the Steady-State Assumption

Introduction: Free radical polymerization plays a vital role in the preparation of polymer materials. A great number of ethylene-based polymer materials are produced by this method. The kinetics of free radical polymerization is one of the most important theories in the field of polymer science. However, this theory, based on the steady-state assumption, is not perfect and is full of controversy. Methods: In this paper, we propose a new approach to calculate the kinetic parameters of free radical polymerization and analyze the characteristics of the polymerization process. Results: The research indicates that the concentration of free radicals increases rapidly over time in the early stage of polymerization and then decreases approximately exponentially. The concentration of free radicals does not remain constant during this process, which suggests the steady-state assumption is not true. Discussion: The rate constant for monomer chain propagation significantly affects the variations in the monomer concentration and kinetic chain length over time. In general, a larger value of the rate constant for chain propagation can cause the monomer concentration and kinetic chain length to decrease more rapidly over time. Similarly, the initiator activity also affects the variations in the monomer concentration and kinetic chain length over time. Higher initiator activity generally results in a faster decrease in the monomer concentration and kinetic chain length. Conclusion: The above discussion comprehensively describes the kinetic characteristics of free radical polymerization, which enables teachers to teach the kinetic theory of free radical polymerization more effectively and improve their teaching level.