Nonadiabatic frontal polymerization

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. In a previous paper, a perfectly insulated tube (i.e., an adiabatic polymerization process) was considered. In reality, it is nearly impossible to eliminate heat losses completely, and an accurate model must take this into account. Extinction of polymerization waves and difficulties initiating the wave, both as a result of heat losses, are often encountered in experiments. This paper will therefore concentrate on nonadiabatic frontal polymerization. The propagation of nonadiabatic free-radical polymerization fronts is studied by methods originally developed in combustion theory, and employed in a previous paper. This analysis is accomplished by examination of the structure of the polymerization wave, its propagation velocity, degree of conversion of the monomer and maximum temperature, and how these quantities are affected by changes in initial temperature, concentrations and kinetic parameters. The values of these quantities near the extinction limit (beyond which traveling-wave solutions will no longer exist) are compared to those in the adiabatic case.