CAS: Development of a General System for Upcycling Polyolefins through C-H Diversification

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Erik J. Alexanian教授正在开发通过C-H键多样化来升级聚烯烃的化学试剂。聚烯烃是一种聚乙烯和聚丙烯热塑性塑料，无毒，耐用，耐热，能够承受大多数化学腐蚀。它们主要由石油和天然气分别通过乙烯和丙烯聚合生产。它们是世界上使用最广泛的塑料，从饮用吸管到复杂的实验室仪器，每种塑料都有多种变体。从化学结构上看，它们是由C-C和C-H键组成的长链碳氢化合物大分子。该项目将通过开发能够使聚烯烃混合物的碳氢化合物选择性多样化的试剂来解决聚烯烃的可持续性和可回收性问题。从本质上讲，通过这种多样化，沿着聚合物主链的C-H基团将被其他有价值的、多样化的化学官能团所取代。从长远来看，与本研究相关的方法有可能为聚烯烃升级回收提供有价值的方法，其中消费后的塑料废物将作为合成具有更大经济价值和更小环境足迹的塑料的丰富原料。亚历山大教授建立的北卡罗来纳大学化学教育外展小组将包括研究生在一系列当地学校教学，特别是那些种族和社会经济高度多样化的学校。这些主题旨在揭示化学及其对我们生活的影响之间的重要联系。此外，通过北卡罗来纳大学莫尔黑德天文馆和科学中心的发射实验室创客空间开展的“聚合物升级回收”外展活动将吸引当地K-12学习者和公众参与构建更可持续的聚合物生命周期的挑战和机遇。该项目将重点开发新型n功能化酰胺和自由基陷阱，使聚烯烃混合物的C-H选择性多样化，并赋予一系列新的聚合物性能。在第一个目标中，将开发新型的o -烯基羟甲酸酯和n -二硫代羰基试剂，以提高平台的实用性，并实现可扩展的、位点选择性的聚烯烃碳氢化合物多样化。第二个目标将侧重于利用这些结构优化的试剂来选择性功能化聚乙烯/聚丙烯混合物，以及与塑料废物流中常见的其他聚合物的混合物。最后，最后一个目标将确定一组不同的硫代磺酸盐作为自由基捕获试剂，以选择性的方式引入一系列功能到聚烯烃上。直接聚烯烃C-H杂芳化也将进行。这项研究开发的工具有可能在与混合塑料废物处理相关的条件下，将聚烯烃升级为一系列新的聚合物。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, Professor Erik J. Alexanian of the University of North Carolina at Chapel Hill is developing chemical reagents for upcycling polyolefins through C-H bond diversification. Polyolefins are a family of polyethylene and polypropylene thermoplastics that are non-toxic, durable, heat resistant, and capable of withstanding most kinds of chemical corrosion. They are produced mainly from oil and natural gas by polymerization of ethylene and propylene, respectively. They are the most widely utilized plastics in the world, with variations of each used in numerous products, ranging from drinking straws to sophisticated laboratory instruments. By chemical structure, they are long chain hydrocarbon macromolecules consisting exclusively of C-C and C-H bonds. This project will address sustainability and recyclability of polyolefins by developing reagents that enable the selective C–H diversification of polyolefin mixtures. Essentially, through such diversification, C-H groups along the main polymer backbone will be replaced with other valuable and diverse chemical functional groups. In the long run, the approaches associated with this research have the potential to provide valuable methods for polyolefin upcycling, where post-consumer plastic waste will serve as an abundant feedstock for the synthesis of plastics with a greater economic value and a smaller environmental footprint. The UNC Chemical Education Outreach group, established by Prof. Alexanian, will involve graduate students teaching at a range of local schools, especially those with high ethnic and socioeconomic diversity. The topics will aim to draw important connections between chemistry and its impact on our lives. Additionally, “Polymer Upcycling” outreach activities through the UNC Morehead Planetarium and Science Center’s Launch Lab Makerspace will engage local K-12 learners and the public on the challenges and opportunities for building more sustainable polymer lifecycles.This project will focus on the development of novel classes of N-functionalized amides and radical traps that enable the selective C–H diversification of polyolefin mixtures and impart a range of new polymer properties. In the first objective, new classes of O-alkenylhydroxamate and N-dithiocarbonyl reagents will be developed to increase the practicality of the platform and enable scalable, site-selective polyolefin C–H diversification. The second objective will focus on utilizing these structurally optimized reagents for the selective functionalization of polyethylene/polypropylene mixtures, and mixtures with other polymers commonly found in plastic waste streams. Finally, the last objective will identify a diverse set of thiosulfonates as radical trapping reagents to introduce a range of functionality onto polyolefins in a selective manner. Direct polyolefin C–H heteroarylation will also be pursued. The tools developed with this research have the potential to enable the upcycling of polyolefins to a range of new polymers under conditions relevant to the processing of mixed plastic waste.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.