On the steady-state approximation in thermal free radical frontal polymerization

Frontal polymerization is a process in which a spatially localized reaction zone propagates into a monomer converting it into a polymer. We formulate a mathematical model of thermal free radical frontal polymerization involvi ng a Eve-species reaction mechanism and justify its reduction to a four-spe cies problem by combining the concentrations of two kinds of radicals, prim ary radicals and polymer radicals. We study the simplified problem both num erically and analytically, and determine such important characteristics of the process as the propagation speed of the wave, the final temperature in the System, and the spatial distributions of all the species in the wave. W e perform the analyses with the steady-state approximation (SSA) and withou t it, and reveal where the SSA solution breaks down. Specifically, the non- SSA solution predicts full monomer conversion and an adiabatic final system temperature, whereas the SSA solution predicts a less-than-adisbatic final temperature and incomplete conversion. (C) 1999 Elsevier Science Ltd. All rights reserved.