Covalent Polymer Mechanochemistry

在NSF化学部大分子、超分子和纳米化学项目的支持下，杜克大学的Stephen克雷格教授正在学习如何决定由机械力加速的化学反应的速率和结果。有机聚合物材料或塑料由于它们在其使用周期期间经历的机械力而分解。聚合物的机械降解限制了它们在轻质结构材料、消费品和生物医学应用中的应用。 因此，对耦合力敏感的反应会影响材料设计的多个方面，包括当前聚合物材料的宏观失效和机械限制。此外，机械响应功能基团可能作为新的应力响应和自修复聚合物材料的关键元素。克雷格教授的研究将深入了解聚合物在使用过程中所经历的宏观机械力如何有效地转化为所需的化学反应，为新型聚合物提供基础。该项目的更广泛影响包括：（1）通过结合本科和高中的研究经验，在化学入门方面开发主动学习模块和相关的实验室经验;（2）通过在年轻科学家的科学生涯早期，在科学领域出现不成比例的自然减员之前，吸引和招募年轻科学家，扩大代表性不足群体的参与;（3）广泛传播研究成果;（4）以一种将对广泛领域产生影响的方式解决分子行为的基本问题，包括聚合物化学，物理有机化学，自修复和应力响应材料。首要的技术目标是通过采用最先进的物理测量和开发新的定量方法，为机械化学动力学奠定定量基础。该研究计划包括直接的，实验表征和量化的机械力对共价反应引发的沿着过度拉伸的聚合物主链的影响。由于机械力，不同于传统形式的能量输入，如热或光，是定向的，机械力和反应性之间的耦合预计将提供洞察过渡态的结构和反应势能面的形状。然而，尽管力对化学反应的影响很重要，但定量测量力对化学反应的影响却很少。这项工作将进一步发展一种新的方法来量化机械化学反应性：用原子力显微镜拉动单分子的多机械基团，不可切割的聚合物。观察到的机械化学活性的模型应该允许定量评估反应性，以及外部因素的影响，如周围环境和光诱导的变化对分子结构的影响。该奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

With the support from the Macromolecular, Supramolecular and Nanochemistry Program of the NSF Chemistry Division, Professor Stephen Craig at Duke University is learning how to dictate the rates and outcomes of chemical reactions that are accelerated by an applied mechanical force. Organic polymeric materials, or plastics, break down due to the mechanical forces they experience during their use cycles. The mechanical degradation of polymers limits their use in lightweight structural materials, consumer products, and biomedical applications. Reactions that are sensitive to a coupled force therefore impact multiple aspects of materials design, including the macroscopic failure and mechanical limitations of current polymeric materials. In addition, mechanically responsive functional groups might serve as the critical elements in new stress-responsive and self-healing polymeric materials. Professor Craig’s studies will provide insight into how the macroscopic mechanical forces experienced by polymers during use can be effectively channeled into desired chemical responses, providing a foundation for new classes of polymers. Broader impacts of the project include: (1) developing active learning modules and associated laboratory experiences in introductory chemistry and through coupled undergraduate and high school research experiences; (2) broadening the participation of underrepresented groups by engaging and recruiting young scientists early in their scientific careers, before the onset of disproportionate attrition from the sciences; (3) disseminating the results of the research broadly; and, (4) addressing fundamental questions of molecular behavior in a manner that will have an impact on a broad range of fields including polymer chemistry, physical organic chemistry, and self-healing and stress-responsive materials. The overarching technical objective is to lay a quantitative foundation for mechanochemical kinetics by employing state-of-the-art physical measurements and developing new methods for quantitation. The research plan includes the direct, experimental characterization and quantification of the effect of mechanical forces on covalent reactions triggered along overstretched polymer backbones. Because mechanical force, unlike conventional forms of energy input such as heat or light, is directional, the coupling between mechanical force and reactivity is expected to provide insights into the structure of transition states and the shapes of reaction potential energy surfaces. Despite its importance, however, quantitative measures of the effect of force on chemical reactions are rare. The proposed work will further develop a novel approach to quantifying mechanochemical reactivity: pulling on single molecules of muti-mechanophore, non-scissile polymers with an atomic force microscope. Models for the observed mechanochemical activity should permit a quantitative assessment of reactivity, and of the influence of external factors such as the surrounding environment and light-induced changes upon molecular structure.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.