Covalent Polymer Mechanochemistry

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。 杜克大学的斯蒂芬克雷格教授正在学习如何决定化学反应的速率和结果，这些反应是由施加的机械力加速的。这些反应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。克雷格教授的研究旨在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）通过新的区域技术培训计划整合研究和教育，支持和丰富主要由本科院校，社区学院，高级高中和小型研究型大学提供的研究活动和科学培训经验;（2）积极的学习模块和相关的实验室经验，在介绍化学和通过耦合本科和高中的研究经验;（3）在科学界出现不成比例的自然减员之前，通过在年轻科学家的科学生涯早期就聘用他们，扩大代表性不足群体的参与;（4）广泛传播研究成果;以及（5）以将对包括聚合物化学，物理有机化学，以及自我修复和压力反应材料。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。具体实验包括机械力对沿沿着过度拉伸的聚合物主链引发的共价反应的影响的直接、实验表征和定量。因为机械力，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提供了对过渡态结构和反应势能面形状的见解。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。该项目旨在开发两种新的方法来量化机械化学反应性：用原子力显微镜拉动多机械基团的单分子，不可切割的聚合物，以及脉冲超声处理和多机械基团的分子量降解，易切割的聚合物。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。

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. Prof. 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. These reactions 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. Prof. Craig's studies aim to 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) integration of research and education through a new, regional technical training program that supports and enriches the research activities and scientific training experiences provided by primarily undergraduate institutions, community colleges, advanced high schools, and smaller research universities; (2) active learning modules and associated laboratory experiences in introductory chemistry and through coupled undergraduate and high school research experiences; (3) 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; (4) disseminating the results of the research broadly; and, (5) addressing fundamental questions of molecular behavior in materials 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. Specific experiments include 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 provides 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. This project aims to develop two novel approaches to quantifying mechanochemical reactivity: pulling on single molecules of multi-mechanophore, non-scissile polymers with an atomic force microscope, and the pulsed sonication and molecular weight degradation of multi-mechanophore, scissile polymers. Models for the observed mechanochemical activity enable quantitative assessment of reactivity in both classes of mechanophores.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.