Development of Stereospecific Controlled/Living Radical Polymerization Using Rationally Engineered Chain-End Capping Agents

在耶鲁大学化学系大分子、超分子和纳米化学项目的支持下，钟明江教授将开发新的方法，通过控制立体化学来高效制备聚合物。聚合物的立体化学源于附着在主骨架上的垂基团的取向，对材料的机械刚度、韧性、热行为、结晶度和溶解度等重要性能有重要影响。调整聚合物的立体化学可以极大地改变其性质，因此可以导致许多聚合物的新应用。然而，目前实现立体化学控制的方法在一定程度上是有限的；有发展新方法的空间。与传统方法相比，该项目旨在建立与更广泛的构建模块兼容的方法，可以在环保溶剂中进行，并为立体控制获取新功能材料提供途径。与该项目相关的研究活动预计将对机械坚固材料的合成以及具有重要生物医学用途的材料产生更广泛的科学影响。相关的教学、指导和推广活动将为不同群体的学员创造受教育的机会。本项目提出了通过自由基聚合合成等规聚合物的新方法。在可控/活性自由基聚合过程中，将合成路易斯酸系稳定自由基，通过限制链端构象来控制聚合物的弹性。一系列稳定的自由基种类将被探索，跨越一系列的反应溶剂和拴链配体，以扩大可聚合单体的空间。钟的研究小组还将研究聚合机制，目的是对这种催化系统有更深入的了解。要研究的机理特征包括Lewis酸与单体单元的配位，自由基加成过程中的链端构象，以及自由基失活过程的动力学和热力学。这些催化剂的成功开发和部署将具有重要意义，特别是因为它们有可能为自由基加成中的立体控制这一重要问题提供一种新的方法。由于自由基聚合相对于需要酸性或碱性条件的聚合条件的优势，该研究也具有潜在的工业化学意义，自由基聚合方法通常表现出更大的官能团耐受性和更温和的反应条件。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 the support of the Macromolecular, Supramolecular, and Nanochemistry Program in the Division of Chemistry, Mingjiang Zhong of Yale University will develop new methods for the efficient preparation of polymers with control of stereochemistry. Stereochemistry of polymers originates from the orientation of pendant groups attached to the main backbone and has a significant influence on important materials properties, including mechanical stiffness, toughness, thermal behavior, crystallinity, and solubility. Tuning the stereochemistry of polymers can dramatically change the properties and therefore can lead to new applications of many polymers. However, currently existing methods to achieve control over stereochemistry are somewhat limited in scope; there is room for new methods development. This project aims to establish methods that are compatible with a broader scope of building blocks compared to traditional approaches, that can be carried out in environmentally friendly solvents, and that provide pathways for stereocontrolled access to new functional materials. The research activities affiliated with this project are expected to have broader scientific impact in the synthesis of mechanically robust materials, as well as materials with important biomedical uses. The associated teaching, mentoring, and outreach activities will create educational opportunities for a diverse group of trainees.This project proposes new approaches to synthesizing isotactic polymers via radical polymerization. Lewis acid-tethered stable radical species will be synthesized to control polymer tacticity via confined chain end conformation in controlled/living radical polymerizations. An array of stable radical species will be explored, across a range of reaction solvents and tethered ligands with the goal of expanding the space of polymerizable monomers. The Zhong research team will also investigate polymerization mechanisms with the aim of developing a deeper understanding of this catalytic system. Among the mechanistic features to be examined are included Lewis acid coordination to monomer units, chain end conformation during radical addition, and the kinetics and thermodynamics of the radical deactivation process. The successful development and deployment of these catalysts would be significant, particularly because they have the potential to provide a new approach to the important problem of stereocontrol in radical addition. This research also has potential industrial chemical implications due to the advantages of radical polymerization over polymerization conditions that require acidic or basic conditions, with radical polymerization approaches generally exhibiting greater functional group tolerance and milder reaction conditions.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.