Expanding Mechanically Mediated Polymerization via Mechanistic Understanding

在化学学部大分子、超分子和纳米化学项目的资助下，芝加哥大学的Aaron P. Esser-Kahn教授正在研究压电催化介导聚合反应的机理和反应性。压电化合物是固体材料，如晶体，某些陶瓷，甚至生物物质，如骨骼，它们具有通过施加机械应力产生电荷的能力。在这项工作中，由锌和氧组成的压电粒子在声波（机械应力）的刺激下产生电荷。然后，带电粒子被用来加速聚合物的形成，其中链端包含碳硫键。这些键是非常独特的，因为它们使聚合物链可逆交联，从而形成具有自建模特性的材料。除了对压电粒子如何加速聚合过程的机理理解之外，还进行了一些研究，以确定其表面组成和晶体结构，使用各种复杂的x射线实验技术。这项研究积极地吸引了广泛年龄范围的学生，重点是高中年龄的孩子。该团队正在进一步开发蓬勃发展的高中暑期“路径”项目，旨在增加寻求STEM学位的大学新生的数量。本文主要研究了压电催化聚合的机理和反应性。压电介导的硫醇烯聚合扩展到包括新的自由基和复分解单体，二硫键的形成，和新的反应性。基于自由基的反应性扩展到包括复合和开环过程。同时，探讨了压电粒子介导聚合活性的机理。结合这两种方法，本研究的结果有可能极大地扩展机械控制聚合的知识，以及通过该技术可获得的单体和聚合物。除了简单地改善聚合物性能外，机械驱动的电子弹射事件可用于通过嵌入压电颗粒介导的还原/氧化过程硬化固体材料，同时作为自报告应变和应力传感器。在苛刻的环境中形成新聚合物的潜力也可以使用机械引发的聚合事件。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

With funding from the Macromolecular, Supramolecular and Nanochemistry Program of the Chemistry Division, Professor Aaron P. Esser-Kahn of University of Chicago is investigating the mechanism and reactivity of polymerization reactions mediated by piezoelectric catalysis. Piezoelectric compounds are solid materials, such as crystals, certain ceramics or even biological matter like bone, which have the ability to generate electrical charge from applied mechanical stress. In this work, piezoelectric particles composed of zinc and oxygen are agitated with sound waves (mechanical stress) to build electric charge. The charged particles are then used to speed up the formation of polymers in which the chain-ends contain carbon-sulfur bonds. These bonds are very unique because they enable reversible cross-linking of polymer chains resulting in the formation of materials with self-modelling properties. In addition to a mechanistic understanding of how piezoelectric particles speed up the polymerization process, several studies are performed to determine their surface composition and crystalline structure using a variety of sophisticated X-ray experimental techniques. This research actively engages students across a broad age range with a focus on high-school age children. The team is further developing burgeoning high-school summer “Pathways” program that aims to increase the number of STEM degree seeking college freshman. This research is focused on mechanistic and reactivity studies of polymerization mediated by piezoelectric catalysis. Piezo-mediated thiol-ene polymerization is extended to include new radical and metathesis monomers, disulfide bond formation, and novel reactivity. Radical based reactivity is expanded to include metathesis and ring-opening processes. In parallel, the mechanism by which piezo-particles mediate polymerization activity is explored. Combining these two approaches, the results of this research have the potential to greatly expand both the knowledge of mechanically controlled polymerization and the monomers and polymers accessible via this technique. Beyond simply improving polymer properties, mechanically driven electron ejection events could be used to harden solid materials through reduction/oxidation processes mediated by embedded piezo particles while serving as self-reporting strain and stress sensors. The potential to form new polymers in demanding environments could also be possible using mechanically initiated polymerization events.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.