Exploring Metal-Free Living Cationic Polymerizations via Reversible Addition-Fragmentation Chain Transfer

合成聚合物(俗称塑料)是具有不同长度的不同分子“弦”的混合物。虽然对于许多应用来说，这样的混合物不会影响聚合物的物理性能，但一些应用要求聚合物具有相同长度的线，以获得特定所需的聚合物性能。北卡罗来纳大学教堂山分校魏友教授的研究小组发现了一种新的聚合方法，用于制备长度分布较窄的聚合物。为了进一步发展方法学，本研究寻求更好地了解聚合过程，以便更好地控制此类分子串的长度。这项研究还试图将合成方法的适用性扩大到各种不同的聚合物。教育、协作和外展是该项目不可或缺的方面。尤教授积极招募代表不足的群体的学生加入他的研究小组。研究生、本科生和高中生通过参与这一跨学科研究项目，接受尖端小分子和聚合物合成方法以及复杂分析技术的培训。尤教授积极参与多项外展活动，包括北卡罗来纳大学科学博览会(北卡罗来纳科学节的一部分)。本次活动是北卡罗来纳大学S单一规模最大的科学外展活动，每年吸引约10,000人参加。此外，尤教授还为高中学生和教师设计了关于聚合物太阳能电池的简短讲座，作为气候飞跃计划的一部分。经典的活性阳离子聚合通过离子(即繁殖的链端)和共价(即静止的链端)物种之间的平衡来实现“活”的特性。相比之下，You教授的实验室最近发现的受控阳离子聚合通过一种全新的机制进行-阳离子链转移机制，类似于传统的可逆加成-断裂链转移(RAFT)自由基聚合。本研究探索并阐明了这一新的阳离子聚合过程的机理。该项目研究了一种新的无金属、质子酸引发和酒精介导的可控阳离子聚合的机理细节。研究人员将这种独特的活性阳离子聚合扩展到聚合各种富含电子的单体，并揭示了应用的光催化剂在受控阳离子筏聚合中的作用。这一奖项反映了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。

Synthetic polymers (commonly known as plastics) are a mixture of different molecular "strings" having different lengths. While for many applications, such a mixture does not impact the physical properties of the polymer, some applications require polymers to have strings of the same length to attain specifically-desired polymer properties. The research group of Professor Wei You at the University of North Carolina Chapel Hill has discovered a new polymerization methodology for preparing polymers that have a narrow distribution of lengths. To further develop the methodology, this research seeks a better understanding of the polymerization process in order to achieve greater control of the lengths of such molecular strings. The research also seeks to broaden the applicability of the synthesis methods to a wide range of different polymers. Education, collaboration, and outreach are integral aspects of this project. Professor You actively recruits students of underrepresented groups into his research group. Graduate, undergraduate, and high school students receive training in cutting-edge small molecule and polymer synthetic methods, along with complex analytical techniques through engaging in this interdisciplinary research project. Professor You is actively involved in a number of outreach activities, including the UNC Science Expo (part of the North Carolina Science Festival). This event is UNC?s single largest science outreach event, attracting approximately 10,000 participants annually. In addition, Professor You has also designed short lectures on polymer solar cells for high school students and teachers brought as part of the Climate LEAP program.The classical living cationic polymerization achieves "living" characteristics via the equilibrium between the ionic (i.e., propagating chain end) and the covalent (i.e., resting chain end) species. In contrast, the controlled cationic polymerization recently discovered in Professor You's laboratory proceeds through an entirely new mechanism - a cationic chain transfer mechanism, analogous to that of the conventional Reversible Addition-Fragmentation Chain Transfer (RAFT) radical polymerization. This research explores and elucidates the mechanism of this new cationic polymerization process. The project investigates the mechanistic details of a new metal-free, protonic acid initiated and alcohol-mediated controlled cationic polymerization. The researchers expand this unique living cationic polymerization into polymerizing various electron-rich monomers, and unveiling the roles of the applied photocatalysts in the controlled cationic RAFT polymerization.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.