Investigations of free-radical frontal polymerization in solid monomer

Dionne Imeldia Fortenberry


This study compares and contrasts the characteristics of self-propagating high-temperature synthesis (SHS) to the characteristics of free-radical frontal polymerization in solid monomer-solid initiator systems. The study investigates the similarities and differences between SHS and free-radical frontal polymerization and how these similarities and differences are involved in the comparison and contrast of the two processes. The effect of reactant particle size on wavefront velocity and front temperature has been previously investigated in many SHS systems. The wavefront velocity and front temperature are inversely proportional to the particle size of the melting reactant. No effect is seen in the frontal polymerization of acrylamide investigated in this study. The difference in results is believed to be because of the significant role of particle surface interactions and localized melting of reactants in SHS. These parameters do not play a significant role in frontal polymerization. The fact that SHS is a stoichiometric process and free-radical polymerization is not also influences the effect of particle size on velocity. The effect of green density, or density of the unreacted pellet, on front velocity and front temperature in frontal polymerization of solid monomer is also investigated and compared to that effect in SHS. In both the frontal polymerization system and SHS systems that employ only solid reactants, increasing green density increases front velocity. An increase in front temperature was also seen upon increase of green density in frontal polymerization. Because both systems are driven by heat diffusion, it would be expected that a higher green density (more tightly-packed sample) would result in less heat loss from the front, which would lead to a increased front velocity. Lower green densities (less tightly-packed samples) result in an increase of heat transfer away from the front and a decrease in front temperature. The effect of dilution of the reactant mixture in frontal polymerization is investigated and compared to the effect in SHS. The effect is similar in both systems. The diluent acts as a heat sink in both processes and lowers the front temperature. The effect of gravity on front propagation is explored in frontal polymerization by performing the reactions under microgravity conditions on NASA flights as was done in SHS systems. (Abstract shortened by UMI.)