Molecular Control of Thermomechanics and Shape-Morphing of Dynamic Covalent Polymer Networks

第一部分：非技术概述：可变形聚合物可以改变这些材料在日常生活中作为家庭和个人护理产品的使用方式，包括食品包装和运动产品。作为对刺激(如温度)的响应，这些聚合物可以在不重新成型的情况下反复重塑，并在产品生命周期结束之前重复使用。可重塑聚合物对于软机器人应用也很有用，因为它们能够通过使用多材料方法对材料运动进行编程。然而，挑战在于如何在控制变形温度和材料自我修复特性的同时，创造出具有最大变形能力的材料。这个项目将利用动态共价键的解离和重新形成的能力，以及这个过程的温度敏感性，来支持可控的材料形状变形。该项目将探索动态键处的化学取代和聚合物材料的其他分子参数(如聚合物的化学特性、动态键数等)的影响。在材料功能上。先进的仪器技术将被用来研究分子运动在材料变形和自我修复性能中的作用。该项目将为参与该项目的研究生、本科生和高中生创造一个肥沃的培训场地。PI将与本科生合作，提供研究经验，并将参与增强多样性和拓展活动，目标是鼓励女性和少数族裔学生在STEM领域继续学习材料科学和职业。PART II：技术总结制造可再加工、可重塑的聚合物材料的能力可以改变商品聚合物的未来，并为先进的生物医学和软机器人应用提供新产品。本项目将研究基于马来酰亚胺-呋喃-迪尔斯-阿尔德(DA)反应的动态共价聚合物网络，旨在揭示开发具有所需热机械和形状变形特性的材料的主要潜在原理。重点将是了解网络结构的分子和结构特征如何决定材料的热、自我修复和形状变形性能。针对目前由2-取代呋喃(2-DAP)制备的DA聚合物(DAP)材料热稳定性低、自愈合性能老化、形状变形控制不足等问题，本项目将解决这些挑战，开发具有实用热稳定性、自愈性和形状变形特性的DAP材料家族。这将通过引入更强的DA交联剂(由呋喃环上的取代控制)和了解网络的分子参数(链刚性、聚合物链长度、缠结的存在)、分子运动和DAP材料的宏观粘弹性之间的关系来实现。该项目将包括利用3-取代氨基呋喃(3-DAP)合成具有更高耐温性的DAP网络，利用DSC、FTIR和核磁共振技术研究DA结的立体化学和热力学，并利用中子反射仪(NR)和光漂白技术探索纠缠对材料热力学性能和自愈性能的贡献。上述研究将为通过网络塑性机制创建可编程变形其永久形状的变形DAP结构奠定基础。该项目的主要成果将是发展与分子参数、DA交联物的立体化学、DAP网络中的分子扩散性以及由此产生的材料自愈合和形状变形特性相关的知识。这一奖项反映了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。

PART I: NON-TECHNICAL SUMMARY Shape-morphing polymers can transform the way these materials are used in everyday life as home and personal care products, including food packaging and sporting products. In response to a stimulus (such as temperature), these polymers can be repeatedly re-shaped without re-molding and re-used prior to the product’s end-of-life. Re-shapable polymers are also useful for soft robotics applications as they enable programming of the material motions via the use of a multi-material approach. The challenges are, however, to create materials with maximized ability for shape changes while controlling the morphing temperature and the materials’ self-healing characteristics. This project will take advantage of the capability of dynamic covalent bonds to dissociate and re-form, and the temperature-sensitivity of this process, to support controllable material shape morphing. The project will explore the effects of chemical substitutions at a dynamic bond and other molecular parameters of polymer materials (such as polymer chemical identity, number of dynamic bonds, etc.) on material functionality. Advanced instrumental techniques will be used to study the role of molecular motion in the material morphing and self-healing properties. The project will create a fertile training ground for participating graduate, undergraduate and high-school students. The PI will work with undergraduate students to provide research experiences and will be engaged in diversity-enhancing and outreach activities with the goal of encouraging female and minority students to pursue studies in materials science and careers in STEM fields.PART II: TECHNICAL SUMMARYThe ability to make re-processable, re-shapable polymer materials can transform the future of commodity polymers and afford novel products for advanced biomedical and soft robotics applications. This project will study dynamic covalent polymer networks based on the maleimide-furan Diels-Alder (DA) reaction and aim to uncover the main underlying principles of developing materials with desired thermomechanical and shape-morphing characteristics. The focus will be on understanding how molecular and structural characteristics of the network determine the materials’ thermal, self-healing and shape-morphing properties. While the current DA polymer (DAP) materials made with 2-substituted furans (2-DAPs) suffer from low thermal stability, aging of their self-healing properties, and insufficient control of shape morphing, this project will address these challenges and develop a new family of DAP materials with practical thermal stability, self-healing and shape-morphing characteristics. This will be achieved by introducing stronger DA crosslinks (controlled by substitution in the furan ring) and understanding of the relationships between molecular parameters of the network (chain rigidity, length of the polymer strands, presence of entanglements), molecular motions and macroscopic viscoelastic properties of DAP materials. The project will involve synthesis of DAP networks using 3-substituted aminofurans (3-DAPs) with improved temperature resistivity, studies of stereochemistry and thermodynamics of DA junctions using DSC, FTIR, and NMR techniques, and exploration of the contributions of entanglements in material thermomechanical properties and self-healing properties using neutron reflectometry (NR) and fluorescence recovery after photobleaching techniques. The above studies will serve as a foundation for creating shape-morphing DAP constructs with programmable morphing of their permanent shape via the mechanism of network plasticity. The main outcome of the project will be the development of the knowledge relating molecular parameters, stereochemistry of DA crosslinks, molecular diffusivity within DAP networks, and the resultant material self-healing and shape morphing characteristics. .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.