Reshaping Recyclable Thermosets

非技术总结许多合成材料的长期持久性及其对环境的影响清楚地表明了开发可持续聚合物的新途径的重要性。该项目旨在通过设计新的、坚固的、寿命更长的材料来应对可持续性的挑战，这些材料需要较少地更换。可回收和自修复材料为延长聚合物材料的使用寿命提供了一条途径。不幸的是，许多最常见的可回收和可修复的聚合物都存在耐溶剂性差或暴露在高温下的问题。相反，具有更高的溶剂、热稳定性和尺寸稳定性的聚合物通常不能回收，也不能自我修复，因为它们的分子结构不允许这样做所需的流动性。这个项目旨在阐明将允许弥合这两个经典的不同材料家族之间的鸿沟的基本原理。通过对关键分子尺度参数的精确控制，将确定控制加工性、可回收性、自愈性和实用性的因素，以便设计下一代材料。这个项目的一个关键组成部分包括针对当地K-12学生的推广和教育活动，以及新兴化学和聚合物科学领域的研究生和本科生的培训和专业发展。技术总结大宗聚合物材料的传统分类机制之一依赖于组成材料的链是否交联。与其非交联型类似物(即热塑性塑料)相比，交联聚合物(即热固性聚合物)的尺寸、化学、机械和溶剂稳定性可能显著提高，但这些属性伴随着不能被重塑或回收。通过依赖可通过缔合或解离机制进行交换的可逆交联物，对结合热固性和热塑性塑料性能的材料有很大的需求。前一种交叉链路交换方法特别有前景，因为它允许在不丢失连接的情况下重新安排网络(即，不改变交叉链路密度)。最近，进行联想交换的网络被称为“刻薄分子”。该项目的目标是研究和开发可通过一种直接方法获得的玻璃化聚合物，这种方法依赖于通过受控自由基聚合生成的乙烯基单体衍生的预聚体的固化。关键是，该策略分离了网络固化和主干聚合步骤，允许精确操纵组成网络的链中的结构、拓扑和功能。我们将致力于三个具体目标：(1)考察乙烯基聚合物玻璃化聚合物的聚合物组分和交联剂组分的结构元素的影响；(2)确定链结构和拓扑结构对玻璃化聚合物(再)加工性能的影响；(3)制备和研究具有可激发活性的本征催化剂的玻璃化聚合物。成功完成这些目标将揭示动态交联网络的基本结构-性质关系，同时生成具有前所未有的化学和机械性能的玻璃剂的设计原则。该奖项反映了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。

NON-TECHNICAL SUMMARYThe long-term persistence of many synthetic materials and the resulting impact on the environment has made clear the importance of developing new routes to sustainable polymers. This project aims to address the challenges of sustainability via the design of new, robust materials with longer life spans that need to be replaced less frequently. Recyclable and self-repairing materials offer one route for extending the useful lifetime of a polymeric material. Unfortunately, many of the most commonly encountered polymers that are readily recyclable and repairable suffer from poor resistance to solvents or exposure to high temperatures. Conversely, polymers with enhanced solvent, thermal, and dimensional stability are generally not recyclable and cannot be rendered self-healing, because their molecular structure does not allow the mobility required to do so. This project aims to elucidate the fundamentals that will allow bridging the divide between these two classically disparate families of materials. By exercising precise control over key molecular-scale parameters, the factors governing processability, recyclability, self-healing, and utility will be determined to allow the design of next-generation materials. A key component of this project involves outreach and educational activities directed toward local K-12 students as well as training and professional development of graduate and undergraduate students in emerging areas of chemistry and polymer science.TECHNICAL SUMMARYOne of the traditional classification mechanisms for bulk polymeric materials relies on whether or not the chains that comprise the material are crosslinked. Crosslinked polymers (i.e., thermosets) may have significantly enhanced dimensional, chemical, mechanical, and solvent stability compared to their non-crosslinked analogs (i.e., thermoplastics), but these attributes are accompanied by an inability to be reshaped or recycled. There is a significant need for materials that combine the properties of thermosets and thermoplastics by relying on reversible crosslinks that can undergo exchange by either an associative or dissociative mechanism. The former method of crosslink exchange is particularly promising because it allows for network rearrangement without loss of connectivity (i.e., no change in crosslink density). Networks that undergo associative exchange have recently become known as "vitrimers." The goal of this project is the investigation and development of vitrimers that are accessible via a straightforward method that relies on the curing of vinyl monomer-derived prepolymers generated by controlled radical polymerization. Critically, this strategy decouples the network curing and backbone polymerization steps, allowing for precise manipulation of structure, topology, and functionality within the chains comprising the network. Three specific aims will be pursued to (1) interrogate the effect of structural elements of both the polymeric and crosslinker components of vitrimers derived from vinyl polymers, (2) determine the role of chain microstructure and topology on vitrimer (re)processability, and (3) prepare and investigate vitrimers with stimuli-activatable intrinsic catalysts. Successful completion of these aims will reveal fundamental structure-property relationships of dynamically crosslinked networks while generating design principles for vitrimers with unprecedented chemical and mechanical properties..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.