CAS-Climate: Mechanically Active Degradable Polymers

在化学系大分子、超分子和纳米化学项目的支持下，阿克伦大学的王俊鹏教授正在开发具有机械活性的可降解聚合物。聚合物，通常被称为塑料，是主要由碳碳键组成的长链大分子。能够在外界刺激下降解的塑料是各种应用的理想选择，包括可拆卸涂层，可回收材料和可修复的电子产品。它们的降解通常是通过在聚合物主链中结合的可降解官能团的裂解而实现的。然而，可降解的官能团也会导致稳定性问题，因为它们可以在环境条件下被触发。该项目将包括一系列聚合物的设计和合成，通过将“锁定”部分引入可降解聚合物来解决稳定性问题。在材料的储存和正常使用过程中，锁紧部分将保持聚合物的骨干完整性和机械性能。当需要降解时，锁定部分将被解锁以实现刺激响应降解。从可持续发展的角度来看，与该项目相关的设计原则为当前广泛使用不可降解乙烯基塑料带来的挑战提供了一个非常有前途和可行的解决方案。因此，开发的方法可以用来制造易于降解的塑料，适合循环经济。这反过来可能会减少对石油、天然气和煤炭等化石燃料的需求，这些燃料是99%以上塑料商品的原材料。由于化石燃料的精炼是密集的，因此也可以实现温室气体排放的显著减少。该项目将为学生提供高度跨学科领域的培训机会，该领域整合了前沿的物理有机化学，有机和聚合物合成以及机械化学。这项研究还将确保在开发新课程、与高中建立伙伴关系以及让代表性不足的群体参与的基础上，为科学与教育的融合提供最大的机会。外展活动将侧重于发展与俄亥俄州历史悠久的黑人学院和大学（HBCUs）的招聘关系，并与阿克伦儿童博物馆合作准备一个名为“聚合物与生活”的展览。该项目将专注于设计和合成一类可以经历两步降解方式的聚合物：机械化学激活，然后是降解。这种降解机制将允许聚合物的降解由机械力控制，并将在保持最佳物理性能的同时提高聚合物的整体稳定性。在第一个目标中，机械载体的反应性将通过取代基效应、立体化学、区域化学和侧链效应来调节。这种方法将提供机械化学结构-活性关系，可以指导下一代刺激响应功能聚合物的设计和开发。第二个目标将集中于不同的降解反应，包括多刺激反应性降解、催化解聚和化学放大降解。所获得的结果将使该系统能够耦合到广泛的应用中，例如控制药物释放，可回收材料，以及响应表面和界面。在第三个目标中，机械活性降解将在溶液相和大块材料中得到证明，这将为聚合物中的应力分布提供重要的见解。此外，这种设计可以通过机械活化降解将热固性塑料转化为热塑性塑料。与该项目相关的新化学有可能实现塑料的有效回收/升级再利用，并促进对聚合物机械化学的理解。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。

With the support of the Macromolecular, Supramolecular, and Nanochemistry Program in the Division of Chemistry, Professor Junpeng Wang at the University of Akron is developing mechanically active degradable polymers. Polymers, commonly referred to as plastics, are long-chain macromolecules that consist of predominantly carbon-carbon bonds. Plastics that can degrade in response to external stimuli are desirable for a variety of applications, including removable coatings, recyclable materials, and repairable electronics. Their degradation is typically enabled by the cleavage of degradable functional groups that are incorporated in the polymer backbone. However, degradable functional groups can also lead to stability issues as they can be triggered under ambient conditions. This project will encompass the design and synthesis of a family of polymers that address the stability issues by introducing “locking” moieties to degradable polymers. A locking moiety will maintain the backbone integrity and mechanical properties of the polymer during storage and normal use of the materials. When degradation is needed, the locking moiety will be unlocked to enable stimuli-responsive degradation. From the sustainability point of view, the design principle associated with this project provides a very promising and viable solution to the current challenges associated with the widespread usage of non-degradable vinyl plastics. Hence, the developed methodology could be utilized to build readily degradable plastics that are amenable to a circular economy. This in turn could decrease demand for fossil fuels, such as oil, gas, and coal, which are the raw materials for over 99% of plastic commodity products. Since the refining of fossil fuels is intensive, a significant reduction in the emission of greenhouse gas could also be achieved. This project will provide training opportunities for students in a highly interdisciplinary area that integrates cutting-edge physical organic chemistry, organic and polymer synthesis, and mechanochemistry. The research will also ensure maximum opportunity for integrating science and education based on new course development, partnerships with high schools, and the involvement of underrepresented groups. Outreach activities will focus on developing recruiting relationships with Historically Black Colleges and Universities (HBCUs) in Ohio and preparing an exhibition “Polymers and Life” in collaboration with Akron Children’s Museum. This project will focus on the design and synthesis of a class of polymers that can undergo a two-step degradation fashion: mechanochemical activation followed by degradation. This degradation mechanism will allow the degradation of the polymers to be controlled by mechanical force and will improve overall polymer stability while retaining optimal physical properties. In the first objective, the reactivity of the mechanophores will be tuned through substituent effects, stereochemistry, regiochemistry, and sidechain effects. This approach will provide mechanochemical structure–activity relationships that can guide the design and development of next-generation stimuli-responsive functional polymers. The second objective will focus on diverse degradation responses, including multi-stimuli responsive degradation, catalytic depolymerization, and chemically amplified degradation. The obtained results will enable the system to be coupled to a broad range of applications, such as controlled drug release, recyclable materials, as well as responsive surface and interface. In the third objective, the mechanically active degradation will be demonstrated in both solution-phase and bulk materials, which will provide important insights into stress distribution in polymers. Moreover, this design can be leveraged to convert thermosets into thermoplastics through mechanically activated degradation. New chemistries associated with this project have the potential to enable efficient recycling/upcycling of plastics and advance understanding of polymer mechanochemistry.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.