Abstract - Pojman - 9319175 An exothermic reaction can sometimes support a propagating front of reaction in an unstirred medium. Polymerization reactions are very exothermic, and addition polymerizations can be initiated with free radicals produced from the thermal decomposition of an unstable compound such as a peroxide. Thus, the heat produced by the polymerization can diffuse and cause the initiation of polymerization in a neighboring region, resulting in a propagating front. Performing polymerization in the frontal regime has, for example, potential for materials synthesis for two reasons: (1) If the polymerization were performed in a flow reactor such that the input flow velocity would equal the front propagation velocity, then it would be possible to maintain the high temperature, strongly oxidizing reaction zone away from the walls. If the oxidizing region is in contact with the metal walls, as in a standard Continuous Stirred Tank Reactor (CSTR), then oxidized impurities will necessarily contaminate the product. However, in the frontal regime, the reaction zone is not in contact with metal and thus, no contamination occurs. It has been possible to produce ultra-pure polystyrene and poly(methyl methacrylate) in a commercial plant using this approach. (2) If the front is carried out in a static medium, then novel materials may be formed because of the self-organizing character of the front. But, instabilities in the fronts can interfere with these approaches. The PI is therefore planning to look at the dynamic behavior of propagating polymerization fronts for four reasons: (1) polymerization fronts offer readily accessible experimental systems to test theories of thermal instabilities in reaction-diffusion systems, including oscillations, spinning modes, period-doubling and chaos; (2) polymerization fronts exhibit interesting convective instabilities, that are poorly understood; (3) polymerization fronts hold promise as a means of materials production but instabilities c an interfere (understanding the conditions that lead to instabilities could allow the design of experimental conditions that eliminate the instabilities or exploit them); and (4) developing complete models of frontal polymerization could provide fundamental understanding of non-steady state polymerization kinetics.
