Study of Thermal Frontal Polymerization Utilizing Reactive and Non-Reactive Additives
Thermal frontal polymerization is a process that involves a propagating front travelling through a monomer/initiator solution and converting monomer into polymer. The effects of different reactive and non-reactive additives on front temperature, front velocity, and pot life were studied in a thermal frontal polymerization system of multifunctional acrylates. One issue with thermal frontal polymerization of acrylate monomers is the amount of smoke and fumes produced due to high front temperatures. The effect of thermally-expandable microspheres was studied utilizing a variety of monomers. Solid additives including fillers, inert phase changer materials, and high thermal conductive fillers were investigated. The addition of liquid additives such as trithiol and plasticizer were also evaluated for their impact on front temperature, front velocity, and pot life. Most of the tested additives lowered front temperature and front velocity and were added until they caused the propagating front to quench. Only thiol affected pot life. Lowering front temperature reduced the amount of smoke produced, thus allowing these systems to be used in commercial settings. Of all of the tested additives, thiol worked best for lowering front temperature and reducing the amount of smoke produced. The behavior of fronts propagating in bifurcated media in which the front had different velocities was studied and compared to behavior predicted by Snell's law. The spatial inhomogeneities of frontal polymerization were studied using Snell's law, and it was demonstrated for the first time that thermal frontal polymerization systems follow Snell's law of refraction.