Development and Study of Structurally-Dynamic Covalent Polymers

第一部分： 非技术概述传统的聚合物或塑料被设计为最小化降解（例如通过共价键的断裂），并且因此在其寿命期间保持其机械性能。这导致了广泛的非常有用的材料（如纤维，塑料和粘合剂），在我们的日常生活中无处不在。这种材料的一个问题是，当它们破裂或降解时，修复或回收它们可能是困难的和/或不具成本效益的。如果塑料可以被利用，这将使他们能够治愈划痕或变形，或者更有效地回收利用。实现这一点的一种方法是将可逆键设计到聚合物结构中，所述可逆键可以在施加相对少量的热或光时断裂并重新形成。有了这笔NSF资金，Rowan团队正在研究一系列不同的刺激响应可逆键，这些键将被纳入聚合物中，并用于获得新类别的响应/适应材料。这些系统的一个关键组成部分是能够系统地控制获得键的可逆特性所需的刺激，这反过来又使它们能够针对不同的应用进行定制。有了这些材料，Rowan集团将专注于开发（1）新型软致动器，其作用类似于“聚合物肌肉”，并为（软）机器人提供应用，（2）材料既具有划痕愈合特性，又具有增强的韧性，以延长其使用寿命，以及（3）按需可逆胶水和粘合剂。这个项目涉及研究生和本科生，当地高中的学生，包括来自芝加哥服务不足和少数民族为主的社区的学生。该项目的综合方法为各级学生提供了一个令人兴奋的学习环境和广泛的研究经验。此外，罗文教授和他的研究小组将为一个名为“大自然的材料”的博物馆外展计划设计新的动手演示，这是克利夫兰自然历史博物馆关于马丁·路德·金博士的“冬季发现日”的一部分。天 该计划旨在（i）让当地社区了解聚合物以及大自然的材料如何帮助我们创造一个可持续的地球，（ii）培训当前的研究生如何与公众和年轻学生进行科学和技术的沟通和教育。 技术概述将动态键（可进行可逆交换）引入聚合物网络赋予材料新的适应性。自适应特性来自网络通过动态键交换改变其结构（和/或组成）的能力，因此被称为结构动态聚合物。取决于结合到网络中的动态粘结的具体类型、位置和量，所得膜将具有可再加工/可再模塑的能力，表现出愈合和/或形状记忆性质，并且甚至为具有增强的韧性、应力松弛和/或自适应粘附能力的材料打开大门。该提案概述了对三种不同类型的结构-动态聚合物的合成以及结构（通过NMR，MALDI-MS，FT-IR，UV，POM和WAXS/SAXS）和机械（流变学，拉伸测试和动态机械热分析）研究，不仅侧重于研究这些系统的基础科学，而且还针对适合薄膜化学的特定动态行为的特定应用。具体来说，Rowan小组将专注于（1）聚（二硫化物），（2）含硫杂迈克尔加成物的聚合物和（3）聚（烷基脲）的合成，表征和研究。虽然聚（二硫化物）网络是已知的，并已被研究作为可愈合的材料，它们的用途，以获得光适应性液晶弹性体是新的。 特别感兴趣的是在访问3D致动膜与这类材料。硫-迈克尔反应在室温下可以是动态的，但迄今为止，这类动态键在聚合物领域很少受到关注。这种键的优点是，它的交换热力学和动力学都可以通过改变烯烃（迈克尔受体）的电子来系统地改变。PI将研究的最后一类动态键是商业上最相关的，并且基于大体积烷基脲。烷基脲在聚氨酯工业中用作封闭（保护）异氰酸酯，其在100°C的温度下解封。PI将瞄准/开发可在较低温度下解封的烷基脲和衍生物。这最后两类材料的目标是开发结构/性能关系，重点是它们的固态机械和自适应性能。

PART 1: NON-TECHNICAL SUMMARYTraditional polymers or plastics have been designed to minimize degradation (e.g. by breaking of covalent bonds) and as such maintain their mechanical properties over their lifetime. This has led to a wide range of very useful materials (such as fibers, plastics and adhesives) that are ubiquitous in our daily lives. One issue with such materials is that when they break or degrade it can be difficult and/or not cost effective to repair or recycle them. What if plastics could be accessed that would allow them to either heal scratches or deformations or to be more efficiently recycled. One way to achieve this is to design into the polymer structure reversible bonds that can be broken and remade upon application of a relatively small amount of heat or light. With this NSF funding the Rowan group is working on a range of different stimuli-responsive reversible bonds that will be incorporated into polymers and used to access new classes of responsive/adaptive materials. A key component of these systems is the ability to systematically control the stimulus required to access the reversible character of the bond which in turn allows them to be tailored for different applications. With these materials the Rowan group will focus on the development of (1) new soft actuators that act like 'polymeric muscles' and offer applications to (soft) robotics, (2) materials that exhibit both scratch-healing characteristics as well as enhanced toughness to extend their useful operational lifetime, and (3) on-demand reversible glues and adhesives. This project involves graduate and undergraduate students, students from local high schools, including students from underserved and predominately minority neighborhoods of Chicago. The integrated approach of this project provides students at all levels with an exciting learning environment and broad research experiences. In addition, Prof. Rowan and his research group will design new hands-on demonstrations for a Museum outreach program entitled "Nature's Materials", which is part of the Cleveland Museum of Natural History's "Winter Discovery Day" on Dr. Martin Luther King Jr. Day. This program aims (i) to expose the local community to polymers and how Nature's materials can help us create a sustainable planet, and (ii) to train current graduate students on how to communicate to and educate the general public and younger students about science and technology.PART 2: TECHNICAL SUMMARYThe introduction of dynamic bonds (that can undergo reversible exchange) into a polymer network imparts new adaptive properties onto the materials. The adaptive properties come from the network's ability to alter its architecture (and/or composition) through dynamic bond exchange and as such have been termed structurally-dynamic polymers. Depending on the specific type, placement and amount of the dynamic bond incorporated into the network the resulting films will have the ability to be re-processable/re-moldable, exhibit healing and/or shape-memory properties, and even open the door to materials that have enhanced toughness, stress relaxation, and/or adaptive adhesion capabilities. This proposal outlines the synthetic as well as structural (via NMR, MALDI-MS, FT-IR, UV, POM and WAXS/SAXS) and mechanical (rheology, tensile testing, and dynamic mechanical thermal analysis) studies on three different classes of structurally-dynamic polymers, focusing not only on investigating the basic science of these systems but also on targeting specific applications that suit the specific dynamic behavior of the film's chemistry. Specifically, the Rowan group will focus on the synthesis, characterization, and investigation of (1) poly(disulfides), (2) thia-Michael adduct-containing polymers and (3) poly(alkylureas). While poly(disulfides) networks are known and have been investigated as healable materials, their use to access photo-adaptive liquid crystalline elastomers is new. Specific interest is in accessing 3D actuating films with this class of material. The thia-Michael reaction can be dynamic at room temperature, but to date, this class of dynamic bond has received little attention in the polymer field. The advantage of this bond is that both its exchange thermodynamics and kinetics can be systematically altered by changing the electronics of the alkene (Michael acceptor). The final class of dynamic bond the PI will investigate is the most commercially relevant and is based on bulky alkylureas. Alkylureas are used as blocked (protected) isocyanates in the polyurethane industry that deblock at temperatures 100°C. The PI will target/develop alkylureas and derivatives that can deblock at lower temperatures. The goal for these last two classes of materials is to develop structure/property relationships focusing on their solid state mechanical and adaptive properties.