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

变形聚合物可以改变这些材料在日常生活中的使用方式，如家庭和个人护理产品，包括食品包装和运动产品。在响应刺激（如温度）时，这些聚合物可以在产品寿命结束之前反复重新成型而无需重新成型并重新使用。可重塑聚合物对于软机器人应用也很有用，因为它们可以通过使用多材料方法对材料运动进行编程。然而，挑战在于创造具有最大形状变化能力的材料，同时控制变形温度和材料的自愈特性。该项目将利用动态共价键离解和重新形成的能力，以及这一过程的温度敏感性，来支持可控的材料形状变形。该项目将探索动态键上的化学取代以及高分子材料的其他分子参数（如高分子化学特性、动态键数等）对材料功能的影响。先进的仪器技术将用于研究分子运动在材料变形和自愈性能中的作用。该项目将为参与的研究生、本科生和高中生创造一个肥沃的训练场地。PI将与本科生合作，提供研究经验，并将参与多样性增强和外展活动，以鼓励女性和少数民族学生攻读材料科学和STEM领域的职业。第二部分：技术概述制造可再加工，可再成型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颖的产品。该项目将研究基于马来酰亚胺-呋喃Diels-Alder （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基本原理。重点将是了解网络的分子和结构特征如何决定材料的热、自修复和形状变形特性。目前用2-取代呋喃（2-DAPs）制成的DA聚合物（DAP）材料存在热稳定性低、自愈性能老化、形状变形控制不足等问题，本项目将解决这些问题，开发出具有实际热稳定性、自愈性和形状变形特性的新型DAP材料家族。这将通过引入更强的DA交联（由呋喃环中的取代控制）和理解网络分子参数（链刚性、聚合物链长度、缠结的存在）、分子运动和DAP材料宏观粘弹性性能之间的关系来实现。该项目将包括使用3-取代氨基呋喃（3-DAPs）合成具有改进电阻率的DAP网络，使用DSC、FTIR和NMR技术研究DA结的立体化学和热力学，以及使用中子反射法（NR）和光漂白技术后的荧光恢复来探索缠结对材料热机械性能和自修复性能的贡献。以上研究将为通过网络可塑性机制创造具有永久形状可编程变形的形状变形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交联的立体化学，DAP网络中的分子扩散率以及由此产生的材料自愈和形状变形特性相关的知识。该奖项反映了美国国家科学基金会的法定使命，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 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.