Reshaping Recyclable Thermosets

许多合成材料的长期持久性及其对环境造成的影响表明了开发可持续聚合物新途径的重要性。该项目旨在通过设计新的、耐用的材料来应对可持续性的挑战，这些材料具有更长的使用寿命，不需要经常更换。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种途径。不幸的是，许多最常见的聚合物是容易回收和修复的遭受差的耐溶剂性或暴露于高温。相反，具有增强的溶剂、热和尺寸稳定性的聚合物通常是不可回收的，并且不能被赋予自修复性，因为它们的分子结构不允许这样做所需的移动性。这个项目旨在阐明的基本原理，将允许弥合这两个经典的不同家庭的材料之间的鸿沟。通过对关键的分子尺度参数进行精确控制，将确定控制加工性、可回收性、自修复性和实用性的因素，以允许设计下一代材料。该项目的一个关键组成部分涉及针对当地K-12学生的推广和教育活动，以及在化学和聚合物科学的新兴领域对研究生和本科生的培训和专业发展。技术概述散装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。交联聚合物（即，热固性材料）与它们的非交联类似物（即，热塑性塑料），但这些属性伴随着不能再成形或再循环。存在对通过依赖于可逆交联来联合收割机热固性塑料和热塑性塑料的性质的材料的显著需求，所述可逆交联可以通过缔合或解离机制进行交换。前一种交联交换方法是特别有前途的，因为它允许网络重新排列而不损失连接性（即，交联密度没有变化）。经历关联交换的网络最近被称为“vitrimers”。“该项目的目标是研究和开发可通过直接方法获得的玻璃化聚合物，该方法依赖于通过受控自由基聚合产生的乙烯基单体衍生的预聚物的固化。重要的是，该策略使网络固化和主链聚合步骤并行，从而允许精确操纵构成网络的链内的结构、拓扑结构和功能。三个具体的目标将追求（1）询问的影响的聚合物和交联剂组分的vitrimer衍生自乙烯基聚合物的结构元素，（2）确定链的微观结构和拓扑结构上的作用vitrimer（再）加工性，和（3）制备和研究vitrimer与刺激活化的固有催化剂。这些目标的成功完成将揭示动态交联网络的基本结构-性能关系，同时产生具有前所未有的化学和机械性能的玻璃化物的设计原则。该奖项反映了NSF的法定使命，并被认为是值得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的支持。

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.