Carbodiimide Ring-opening Metathesis Polymerization: Precision Synthesis of Nitrogen-Rich Polymer Backbones

碳二亚胺开环复分解聚合：富氮聚合物主链的精密合成

• 批准号: 2203499
• 负责人: Aleksandr Zhukhovitskiy
• 金额: $ 46.5万
• 依托单位: University of North Carolina at Chapel Hill
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-07-01 至 2025-06-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2203499&HistoricalAwards=false
• 关键词: Carbodiimide; Ring; opening; Metathesis; Polymerization

With the support of the Macromolecular, Supramolecular and Nanochemistry program in the Division of Chemistry, Aleksandr Zhukhovitskiy of the University of North Carolina at Chapel Hill is developing ring-opening polymerization reactions for the synthesis of nitrogen-rich polymer backbones. Polymers—macromolecular constituents of plastics and rubber materials— are essential and ubiquitous in our daily lives: from food packaging to clothing to vehicle parts. The vast majority of plastics that are currently being produced contain predominantly carbon atoms along the main polymer backbone. Meanwhile, further developing the chemistry associated with systems containing nitrogen-rich polymer backbones is critically needed. This improved control over their assembly, folding, thermodynamic and dielectric properties, as well as catalytic activity. These concepts are illustrated well in proteins, which are naturally occurring polymers. However, incorporation of nitrogen into the polymer backbone is difficult to achieve synthetically, and the majority of current methodologies are non-selective and generally lack structural precision. In this research, highly active catalysts based on iridium metal will be used in ring-opening polymerization of a variety of carbodiimides to prepare polymers with abundant and precisely positioned nitrogen atoms along the polymer backbone. Strong emphasis will be placed on detailed kinetic and mechanistic understanding of the catalytic cycle, monomer design, and control over the length of polymer chains. Complementary computational methods will also be utilized to guide experimental design and understand how these reactions work and how to improve them. This research provides unique opportunities to educate students in mechanistic analysis, physical organic chemistry, organometallic chemistry and polymer chemistry. The research will also transform the design and synthesis of academically and industrially relevant nitrogen-rich polymer backbones, opening the door to a deeper understanding of the structure-property relationships in these polymers. In addition, the team will continue to expand its educational polymer-chemistry focused program that targets K-12 students and science teachers with a focus on talent pools that remain under-resourced and underrepresented in the STEM fields. This program includes virtual and in-person science demonstrations at K-12 schools in Chapel Hill and will expand to include Durham, NC. These efforts will be instrumental to nurturing within future generations of students an appreciation for and identification with polymer science research.This research will focus on carbodiimide ring-opening metathesis polymerization (CDI ROMP) catalyzed by iridium guanidinate complexes for the precise synthesis of nitrogen-rich polymer backbones. The first objective will focus on the investigation of the reaction mechanism through a combination of experimental and theoretical tools. The following aspects will be explored: verification of chain growth, the type of metathesis process, energetics of the carbodiimide-iridium coordination, the nature of energy barrier of turnover limiting step, and the geometry of the corresponding transition state. Controlled and living CDI ROMP will be developed in the second objective and utilized to prepare block copolymers. Computational and experimental studies will shed light on the effect of ancillary cyclopentadienyl ligand structure in the iridium catalyst on the backbiting/chain transfer process. The last objective will focus on the derivatization of precise main-chain polycarbodiimides to form libraries of other classes of nitrogen-rich polymer backbones, including polyureas, polythioureas, polyguanidines, polyamidines and polyamidinates. The mechanism of insertion/elimination in this research is fundamentally different from traditional metathesis of C-C bonds that proceeds via cyclo-addition/elimination. As such, the gained mechanistic insights will be instructive in the future development of other types of metathesis transformations, such as diazene metathesis and ring-closing carbodiimide metathesis.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.

在化学系大分子、超分子和纳米化学项目的支持下，北卡罗来纳大学教堂山分校的Aleksandr Zhukhovitskiy正在开发用于合成富氮聚合物骨架的开环聚合反应。聚合物——塑料和橡胶材料的大分子成分——在我们的日常生活中是必不可少的，无处不在：从食品包装到服装再到汽车零部件。目前生产的绝大多数塑料主要是由碳原子组成的。与此同时，迫切需要进一步开发与含有富氮聚合物骨架的系统相关的化学。这改善了对其组装、折叠、热力学和介电性能以及催化活性的控制。这些概念在蛋白质中得到了很好的说明，蛋白质是天然存在的聚合物。然而，将氮结合到聚合物主链中是很难实现的，而且目前大多数方法都是非选择性的，通常缺乏结构精度。在本研究中，基于金属铱的高活性催化剂将用于多种碳二亚胺的开环聚合，以制备具有丰富且沿聚合物主链精确定位的氮原子的聚合物。重点将放在催化循环、单体设计和聚合物链长度控制的详细动力学和机理理解上。补充计算方法也将用于指导实验设计，了解这些反应是如何工作的，以及如何改进它们。这项研究提供了独特的机会来教育学生在机械分析，物理有机化学，有机金属化学和聚合物化学。该研究还将改变学术界和工业界相关的富氮聚合物骨架的设计和合成，为深入了解这些聚合物的结构-性能关系打开大门。此外，该团队将继续扩大其以教育聚合物化学为重点的项目，目标是K-12学生和科学教师，重点关注在STEM领域资源不足和代表性不足的人才库。该项目包括在教堂山的K-12学校进行虚拟和面对面的科学演示，并将扩展到北卡罗来纳州的达勒姆。这些努力将有助于培养未来几代学生对聚合物科学研究的欣赏和认同。本课题主要研究胍苷酸铱配合物催化碳二亚胺开环复分解聚合（CDI ROMP），以精确合成富氮聚合物骨架。第一个目标将集中在通过实验和理论工具相结合的反应机理的研究。以下方面将探讨：链生长的验证，复分解过程的类型，碳二亚胺-铱配位的能量学，周转限制步骤的能量势垒性质，以及相应过渡态的几何形状。第二个目标将开发可控和活的CDI ROMP，并用于制备嵌段共聚物。计算和实验研究将揭示铱催化剂中辅助环戊二烯配体结构对背咬链转移过程的影响。最后一个目标将集中在精确的主链聚碳二亚胺衍生化，以形成其他类富氮聚合物骨架，包括聚氨酯，聚硫脲，聚胍，聚酰胺和聚酰胺酸酯。本研究中的插入/消除机制与传统的通过环加成/消除进行的C-C键复合有本质的不同。因此，所获得的机理见解将对其他类型的复分解转化的未来发展具有指导意义，例如重氮的复分解和闭合环的碳二亚胺的复分解。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。

项目成果

Carbodiimide Ring-Opening Metathesis Polymerization.

• DOI: 10.1021/acscentsci.3c00032
• 发表时间: 2023-06-28
• 期刊: ACS CENTRAL SCIENCE
• 影响因子: 18.2
• 作者: Johnson, J. Drake;Kaplan, Samuel W.;Toth, Jozsef;Wang, Zian;Maw, Mitchell;Sheiko, Sergei S.;Zhukhovitskiy, Aleksandr V.
• 通讯作者: Zhukhovitskiy, Aleksandr V.