Macromolecular Metamorphosis: Transformable Polymeric Materials

非技术概述：本项目旨在通过考虑可变形分子形状对最终材料性能的影响，在材料科学领域开发一种新的范式。聚合物分子的结构直接影响它们所用材料的性质。聚合物被设计成具有为特定应用选择的特征和静态分子结构。该项目涉及由可逆键组成的聚合物的开发和研究，这些聚合物在触发时能够在其结构中实现戏剧性的变化。这一概念在响应性聚合物材料领域引入了一种新的范式。由此产生的聚合物将在结构上坚固耐用，同时也允许在损坏时自我修复。刺激响应材料的应用正在不断开发，在药物输送、智能涂层和自我修复材料领域显示出巨大的前景。在溶液中发生结构转变的聚合物可能作为机油或个人护理产品的添加剂具有潜在的用途。在高温下固定之前表现出自我修复和可回收利用的材料可以解决许多通过可逆连接构建的材料的基本限制之一，即它们随时间缓慢变形的倾向。该项目还包括针对当地K-12学生的推广和教育活动，以及对新兴化学和聚合物科学领域的研究生和本科生的培训。技术摘要：目前，大多数刺激响应性聚合物的例子都是通过改变链构象或聚合物-溶剂或聚合物-聚合物相互作用来改变分子大小而产生反应的。然而，分子结构的基本特征通常不被认为是一个变量，因为一个大分子的拓扑结构被它的共价一级结构“锁定”。这个项目通过研究在外部刺激下改变其共价结构的材料来挑战这一惯例。通过制备能够将不可逆键转换为可逆键的聚合物，可以获得一类通过共价结构的转变来适应环境的新型响应材料。具体地说，正在考虑三个系统：(1)能够在溶液中进行拓扑变换的大分子；(2)可改变其共价结构的适应性有机凝胶；以及(3)具有“可切换”交联性的可变形块状材料。第一个系统涉及具有复杂链结构的聚合物，当触发时，这些聚合物不可逆转地转变为新的结构。第二个和第三个系统涉及结构动态的可逆交联型聚合物网络，这意味着它们可以被触发以显著地重新排列其内部结构，从而成为不可逆交联型(即“固定”)。这三个领域被选择来研究这种方法在广泛的尺寸(纳米到宏观)和材料状态(溶液、凝胶和块状)的范围内的潜力，并极大地扩展刺激响应材料的定义。

NON-TECHNICAL SUMMARY:This project seeks to develop a new paradigm in the area of materials science by considering the effects of transformable molecular shape on final materials properties. The architecture of a polymer molecule directly affects the properties of the materials they are used to prepare. Polymers are designed to have a characteristic and static molecular structure selected for a specific application. This project involves the development and investigation of polymers composed of reversible bonds that enable dramatic transformations in their architecture when triggered. This concept introduces a new paradigm in the field of responsive polymeric materials. The resulting polymers will be structurally robust while also allowing themselves to be healed when damaged. Applications of stimuli-responsive materials are continually being developed, with significant promise having been demonstrated in the area of drug delivery, smart coatings, and self-healing materials. Polymers that undergo architectural transformations in solution may have potential utility as additives in motor oil or personal care products. Materials that demonstrate self-healing and recyclability before being fixed at elevated temperatures could address one of the fundamental limitations of many materials constructed via reversible linkages, namely their propensity to slowly deform over time. The project also includes outreach and education activities directed toward local K-12 students and training of graduate and undergraduate students in emerging areas of chemistry and polymer science.TECHNICAL SUMMARY:Currently, most examples of stimuli-responsive polymers derive their response from changes in molecular size through alterations of chain conformation or changes in polymer-solvent or polymer-polymer interactions. However, the fundamental characteristic of molecular architecture has not typically been considered a variable because a macromolecule's topology is "locked" by its covalent primary structure. This project challenges this convention by investigating materials that transform their covalent architecture when triggered by an external stimulus. By preparing polymers capable of exchanging irreversible bonds for reversible bonds, a new class of responsive materials that adapt to their surroundings by transitions in their covalent architecture can be achieved. Specifically, three systems are being considered: (1) macromolecules capable of topological transformations in solution; (2) adaptable organogels that modify their covalent structure; and (3) transformable bulk materials with "switchable" crosslinks. The first system involves polymers with complex chain architectures that irreversibly transform into new architectures when triggered. The second and third systems involve reversibly-crosslinked polymer networks that are structurally-dynamic, meaning they can be triggered to significantly rearrange their internal structure to become irreversibly crosslinked (i.e., "fixed"). These three areas have been chosen to investigate the potential of this approach across a wide spectrum of sizes (nano to macro) and material states (solution, gels, and bulk) and to dramatically expand the definition of stimuli-responsive materials.