Exploring room temperature dynamic covalent bonds in adaptive materials

聚合物/塑料在我们日常生活的几乎每个方面都发挥着关键作用。一般来说，日常使用的大多数塑料是被动的，也就是说，设计用于单一目的（例如，食品容器、塑料袋或粘合剂），并且一旦使用，这些塑料就被扔掉并影响环境。该项目的重点是开发一类自适应聚合物，这些聚合物具有按需愈合或改变形状的能力。此外，这些材料具有在使用后再加工的能力，并且通过控制再加工期间采用的温度和时间，可以定制它们的物理性质（例如，刚度、弹性、温度响应）。精确重组材料特性的能力为目标材料打开了大门，这些材料可以通过加工轻松系统地改变，这反过来又扩大了它们可以用于的潜在应用领域。该研究是聚合物领域内不同学科的混合，从化学到聚合物加工和机械表征。重要的是，这种广泛的研究方法为学生（各级）提供了涵盖这一系列主题的广泛的教育经验。研究生将参加为期两年的外展培训计划，以发展和完善他们的能力，参与和有效地与公众沟通。利用这种培训，他们将参加一系列的推广活动，包括少年科学咖啡馆，不小的问题分子工程博览会，以及一些旨在推广到当地芝加哥公立学校的学生的计划。这些推广活动，结合额外的综合高中和本科生的研究机会，旨在增加科学和工程中代表性不足的少数民族的比例。第二部分：Rowan小组最近的工作已经表明，室温动态thia-Michael（tM）化学（基于苄叉氰基乙酸酯/酰胺迈克尔受体）可以用于通过称为动态反应诱导相分离（DRIPS）的方法来获得机械稳健的聚合物网络。这些相分离的动态材料表现出诸如愈合、形状记忆和可逆粘附的性质。此外，交换动力学和热力学的tM反应可以系统地改变的tM受体的电子性质，允许调查的动态交换性能如何影响相分离的形态和网络的整体材料性能。计划中的研究通过退火条件，曝光和与其他动态键合系统的交叉反应来研究动态tM材料的操作。此外，这些材料的相分离形态（以及因此的机械性能）可以通过热加工条件（冷却速率、退火步骤等）直接操纵。 因此，这项工作的第一个目标是在这类自适应材料中开发基本的结构/加工/形态/性能关系。本工作的第二个目标是开发光响应动态tM键，利用固有的E/Z异构体的苄叉氰基乙酸酯/酰胺迈克尔受体结构，以获得一类新的光活化动态材料。最后，将启动一个新的计划，旨在使用系统聚合物科学方法（受系统化学的启发）进行功能聚合物设计，目标是获得多能聚合物，即聚合物系统，其特性可以在暴露于化学或环境线索时显着改变，使其能够用于各种应用。为此，PI将研究将多个通信动态反应循环纳入聚合物网络的潜力。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。

PART 1: NON-TECHNICAL SUMMARY Polymers/plastics play a critical role in almost every aspect of our daily life. Generally, most plastics in everyday use are passive, that is, designed for a single purpose (e.g., food containers, plastic bags, or adhesives) and once used these plastics are thrown away and impact the environment. This project is focused on developing a class of adaptive polymers that have the ability to heal or change shape on demand. In addition, these materials have the ability to be reprocessed after use, and by controlling the temperature and time employed during reprocessing it is possible to tailor their physical properties (e.g., stiffness, elasticity, temperature response). The ability to precisely retool the material properties opens the door to targeting materials that can be easily and systematically changed by processing, which in turn expands the potential applications areas that they can be used for. The research is a mix of different disciplines within the polymer area, from chemistry to polymer processing and mechanical characterization. Importantly, this broad research approach provides students (at all levels) with wide-ranging educational experiences covering this swath of topics. Graduate students will participate in a two-year outreach training program to develop and refine their abilities to engage and effectively communicate with the general public. Using this training they will participate in a series of outreach events, including Junior Science Cafés, the No Small Matter Molecular Engineering Fair, as well as a number of programs aimed at outreach to students from local Chicago public schools. These outreach activities, in conjunction with additional integrated high-school and undergraduate research opportunities, are designed to increase the fraction of underrepresented minorities in science and engineering. PART 2: TECHNICAL SUMMARY Recent work by the Rowan group has shown that room temperature dynamic thia-Michael (tM) chemistry (based on benzalcyanoacetate/amide Michael acceptors) can be used to access mechanically robust polymer networks through a process coined dynamic reaction-induced phase separation (DRIPS). These phase separated dynamic materials exhibit properties such as healing, shape memory, and reversible adhesion. Furthermore, the exchange kinetics and thermodynamics of tM reactions can be systematically altered by the electronic nature of the tM acceptor, allowing an investigation of how the dynamic exchange properties impact both the phase-separated morphology and the overall materials properties of the network. The planned research investigates the manipulation of dynamic tM materials through annealing conditions, light exposure, and cross-reactivity with additional dynamic bonding systems. In addition, the phase separated morphology (and therefore mechanical properties) of these materials can be directly manipulated through thermal processing conditions (cooling rates, annealing steps, etc.). As such, the first goal of this work is aimed at developing fundamental structure / processing / morphology / property relationships in this class of adaptive materials. The second goal of this work is to develop photo-responsive dynamic tM bonds by taking advantage of the inherent E/Z isomerism of the benzalcyanoacetate/amide Michael acceptor structure, to give access to a new class of photo-activated dynamic materials. Finally, a new program will be initiated aimed at using a Systems Polymer Science approach (inspired by systems chemistry) to functional polymer design with the goal of accessing pluripotent polymers, namely polymer systems whose properties can be significantly altered upon exposure to chemical or environmental cues allowing them to be used in a wide variety of applications. To do this, the PI will investigate the potential of incorporating multiple communicating dynamic reaction cycles into polymer networks..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.