Modeling the kinetics of step homopolymerization reactions--an assessment of different approaches

A critical analysis of two models used to describe the kinetics of step homopolymerization has been undertaken. The classical second-order kinetic model and the more widely adopted Mathew et al. oligomer precipitation model were tested against data published in the literature. The classical model, which predicts an identical molecular weight distribution to that obtained by Flory using a statistical approach, is based on a single rate constant and provided an excellent fit (R²>0.99) to the experimental data. Derived rate constants exhibited logical trends. The Mathew et al. oligomer precipitation model, on the other hand, requires three fitting parameters. This model also fitted the data well but in many cases yielded either negative rate constants for the purported termination step or illogical parametric trends. It was concluded that the classical model was superior to the precipitation model in describing the kinetics and reaction mechanisms of step homopolymerization.