Mathematical modeling of free-radical polymerization fronts

Frontal polymerization is a process in which a spatially localized reaction zone propagates into a monomer, converting it into a polymer. In the simplest case of free-radical polymerization, a mixture of a monomer and initiator is placed into a test tube. Upon reaction initiation at one end of the tube, a self-sustained thermal wave, in which chemical conversion occurs, develops and propagates through the tube. We develop a mathematical model of the frontal polymerization process and analytically determine the structure of the polymerization wave, the propagation velocity, maximum temperature, and degree of conversion of the monomer. Specifically, we examine their dependence on the kinetic parameters of the reaction, the initial temperature of the mixture, and the initial concentrations of the initiator and monomer. Our analytic results are in good quantitative agreement with both direct numerical simulations of the model and experimental data (on butyl acrylate polymerization), which are also presented in the paper.