The Dynamics of Propagating Polymerization Fronts

传播聚合前沿的动力学

• 批准号: 9319175
• 负责人: John Pojman
• 金额: $ 12.78万
• 依托单位: University of Southern Mississippi
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1994
• 资助国家: 美国
• 起止时间: 1994-05-15 至 1997-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9319175&HistoricalAwards=false
• 关键词: Dynamics; Propagating; Polymerization; Fronts

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.

放热反应有时可以在未搅拌的介质中支持反应的传播前沿。聚合反应是非常放热的，加成聚合反应可以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，聚合产生的热量可以扩散，并在邻近区域引发聚合，从而产生传播锋。例如，在正面体系中进行聚合具有材料合成的潜力，原因有两个：(1)如果聚合在流动反应器中进行，使得输入流速等于正面传播速度，那么就有可能保持高温，强氧化反应区远离壁面。如果氧化区与金属壁接触，如在标准的连续搅拌槽式反应器（CSTR）中，则氧化杂质必然会污染产品。然而，在正面制度下，反应区不与金属接触，因此，没有污染发生。用这种方法在商业工厂生产超纯聚苯乙烯和聚甲基丙烯酸甲酯已经成为可能。(2)如果锋面是在静态介质中进行的，那么由于锋面的自组织特性，就有可能形成新的材料。但是，锋面的不稳定会干扰这些方法。因此，PI计划研究传播聚合前沿的动态行为，原因有四个：(1)聚合前沿提供了易于访问的实验系统，以测试反应扩散系统的热不稳定性理论，包括振荡、自旋模式、周期加倍和混沌；(2)聚合锋表现出有趣的对流不稳定性，这一点人们知之甚少；(3)聚合前沿有望成为一种材料生产手段，但不稳定性可能会干扰（了解导致不稳定性的条件可以允许设计实验条件，消除不稳定性或利用它们）；(4)建立完整的正面聚合模型可以为非稳态聚合动力学提供基础认识。