Development and Study of Structurally-Dynamic Covalent Polymers

第1部分：非技术总结传统聚合物或塑料被设计为最大限度地减少降解(例如，通过破坏共价键)，并因此在其生命周期内保持其机械性能。这导致了广泛的非常有用的材料(如纤维、塑料和粘合剂)，这些材料在我们的日常生活中无处不在。这类材料的一个问题是，当它们损坏或降解时，修复或回收它们可能很困难和/或不划算。如果可以接触到塑料，使其能够治愈划痕或变形，或者更有效地回收利用，会发生什么？实现这一点的一种方法是在聚合物结构中设计可逆键，这些键可以在施加相对少量的热或光时断开和重新生成。利用NSF的这笔资金，罗文团队正在研究一系列不同的刺激响应可逆键，这些可逆键将被合并到聚合物中，并用于获得新的响应/适应材料类别。这些系统的一个关键组成部分是能够系统地控制获得债券可逆性所需的刺激，这反过来又允许它们针对不同的应用而量身定做。有了这些材料，罗文团队将专注于(1)新型软执行器的开发，这种软执行器的作用类似于‘聚合肌肉’，并可用于(软)机器人；(2)既表现出划痕愈合特性又能增强韧性以延长其有效使用寿命的材料，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，来自当地高中的学生，包括来自芝加哥服务不足和以少数族裔为主的社区的学生。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，Rowan教授和他的研究小组将为博物馆名为“自然材料”的推广项目设计新的动手演示，该项目是克利夫兰自然历史博物馆在小马丁·路德·金博士日举行的“冬季发现日”的一部分。天。该计划的目的是(I)让当地社区接触聚合物，以及大自然的材料如何帮助我们创造一个可持续的地球，以及(Ii)培训现有的研究生如何与普通公众和年轻学生进行科学和技术方面的交流和教育。第2部分：技术总结将动态键(可以进行可逆交换)引入聚合物网络，赋予材料新的适应性。自适应性能来自于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。根据结合到网络中的动态结合的具体类型、位置和数量，所得到的薄膜将具有可重新加工/重新模塑的能力，表现出愈合和/或形状记忆性能，甚至为具有增强韧性、应力松弛和/或自适应粘合能力的材料打开大门。这份建议概述了三种不同类别的结构动态聚合物的合成和结构研究(通过核磁共振、MALDI-MS、FT-IR、UV、POM和WAXS/SAXS)和力学研究(流变学、拉伸测试和动态机械热分析)，不仅侧重于研究这些体系的基础科学，还着眼于适合薄膜化学特定动态行为的特定应用。具体地说，罗文小组将专注于(1)聚二硫化物、(2)含硫-迈克尔加合物聚合物和(3)聚烷基脲的合成、表征和研究。虽然多(二硫化物)网络是已知的，并已被研究为健康材料，但它们用于获得光适应性液晶弹性体是新的。特别感兴趣的是使用这种材料访问3D致动电影。Thia-Michael反应在室温下可以是动态的，但到目前为止，这类动态键在聚合物领域中很少受到关注。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最具商业意义的，以大体积烷基脲为基础。烷基脲在聚氨酯工业中用作封闭(受保护)的异氰酸酯，在100°C下解封。PI将瞄准/开发能够在较低温度下解封的烷基脲及其衍生物。最后这两类材料的目标是发展结构/性能关系，重点是它们的固态、机械和适应性特性。

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.