Covalent Polymer Mechanochemistry

在美国国家科学基金会化学部大分子、超分子和纳米化学项目的支持下，杜克大学的斯蒂芬·克雷格教授正在学习如何决定由外加机械力加速的化学反应的速度和结果。有机聚合物材料，或塑料，由于它们在使用周期中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破坏和力学限制。此外，机械响应性官能团可能是新型应力响应性和自愈性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引导到所需的化学反应中，从而为新类别的聚合物奠定基础。该项目的更广泛的影响包括：(1)开发化学入门课程的积极学习模块和相关的实验室经验，并通过本科和高中的研究经验相结合；(2)通过在科学生涯早期，在科学上出现不成比例的自然减员之前，吸引和招募年轻科学家，扩大未被充分代表的群体的参与；(3)广泛传播研究结果；以及(4)以将对聚合物化学、物理有机化学、自我修复和压力响应材料等广泛领域产生影响的方式解决分子行为的基本问题。主要的技术目标是通过使用最先进的物理测量和开发新的定量方法，为机械力化学动力学奠定量化基础。研究计划包括直接、实验表征和量化机械力对沿过度拉伸的聚合物主链引发的共价反应的影响。由于机械力与热或光等传统形式的能量输入不同，它是方向性的，机械力和反应性之间的耦合有望提供对过渡态结构和反应势能面形状的洞察。然而，尽管力对化学反应的影响很重要，但对其影响的定量测量却很少。这项拟议的工作将进一步开发一种量化机械力化学反应的新方法：用原子力显微镜拉动多机械团、非剪刀聚合物的单分子。观察到的机械力化学活动的模型应允许对反应性以及外部因素(如周围环境和光诱导的变化对分子结构的影响)的影响进行定量评估。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.