The Dynamics of Propagating Polymerization Fronts

摘要- Pojman - 9319175 放热反应有时可以在未搅拌的介质中支持反应前沿的传播。 聚合反应是非常放热的，并且加成聚合可以用由不稳定化合物如过氧化物的热分解产生的自由基引发。 因此，由聚合产生的热可以扩散并引起相邻区域中的聚合引发，从而导致传播前沿。 例如，由于两个原因，在前沿区进行聚合具有材料合成的潜力：（1）如果聚合在流动反应器中进行，使得输入流速等于前沿传播速度，则可以保持高温、强氧化反应区远离壁。 如果氧化区域与金属壁接触，如在标准的连续搅拌釜式反应器（CSTR）中，则氧化的杂质必然会污染产物。 然而，在正面区域中，反应区不与金属接触，因此不会发生污染。 它已经有可能生产超纯聚苯乙烯和聚（甲基丙烯酸甲酯）在商业工厂使用这种方法。 (2)如果前沿在静态介质中进行，则由于前沿的自组织特性，可以形成新的材料。 但是，前线的不稳定性会干扰这些方法。 因此，PI计划研究传播聚合前沿的动力学行为，原因有四：（1）聚合前沿提供了容易获得的实验系统，以测试反应扩散系统中的热不稳定性理论，包括振荡，旋转模式，倍周期和混沌;（2）聚合前沿表现出有趣的对流不稳定性，这是知之甚少;（3）聚合前沿有望作为材料生产的一种手段，但不稳定性可能会干扰（理解导致不稳定性的条件可以允许设计消除不稳定性或利用它们的实验条件）;和（4）开发前沿聚合的完整模型可以提供对非稳态聚合动力学的基本理解。

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.