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起着至关重要的作用。一般来说，日常使用的大多数塑料都是被动式的，即为单一目的而设计的（例如，食品容器，塑料袋或粘合剂），一旦使用这些塑料就被扔掉并影响环境。这个项目的重点是开发一种自适应聚合物，这种聚合物具有根据需要愈合或改变形状的能力。此外，这些材料在使用后具有再加工的能力，并且通过控制再加工期间使用的温度和时间，可以定制其物理特性（例如，刚度，弹性，温度响应）。精确重组材料特性的能力为可以通过加工轻松系统地改变目标材料打开了大门，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不同学科的结合，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）提供了涵盖这一主题的广泛教育经验。研究生将参加一个为期两年的拓展培训计划，以发展和完善他们与公众接触和有效沟通的能力。通过这次培训，他们将参加一系列的拓展活动，包括青少年科学研讨会、“无关紧要的分子工程博览会”，以及一些旨在拓展芝加哥当地公立学校学生的项目。这些外展活动，加上额外的综合高中和本科研究机会，旨在增加在科学和工程领域代表性不足的少数民族的比例。Rowan小组最近的工作表明，室温动态thia-Michael （tM）化学（基于苯甲氰乙酸酯/酰胺Michael受体）可以通过一种称为动态反应诱导相分离（DRIPS）的过程来获得机械坚固的聚合物网络。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等特性。此外，tM反应的交换动力学和热力学可以被tM受体的电子性质系统地改变，从而允许研究动态交换性质如何影响相分离形态和网络的整体材料性质。计划中的研究通过退火条件、光暴露和与其他动态键合系统的交叉反应性来研究动态tM材料的操作。此外，这些材料的相分离形态（因此机械性能）可以通过热加工条件（冷却速度，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发展基本的结构/加工/形态/性质关系。本研究的第二个目标是利用苯甲氰乙酸酯/酰胺Michael受体结构固有的E/Z异构性来开发光响应动态tM键，从而获得一类新的光激活动态材料。最后，将启动一个新的项目，旨在使用系统聚合物科学方法（受系统化学的启发）来设计功能聚合物，目标是获得多能聚合物，即聚合物系统的性质可以在暴露于化学或环境线索时显着改变，从而使它们能够用于各种应用。为了做到这一点，PI将调查将多个通信动态反应周期纳入聚合物网络的潜力。该奖项反映了NSF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。

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.