EAGER: Autonomous Self-Healing of Commodity Acrylic Copolymers

非技术概述：聚合物表现出丰富的有用特性，使这些材料独特地适用于技术和社会的所有领域的广泛应用。如果商品聚合物能够在骨折后自我修复，就可以寻求许多新的应用，从而实现持久的性能、新的功能和大量的节省。本项目旨在了解观察到的一种商品聚合物(以丙烯酸酯为基础的共聚物)的自我修复行为，这种聚合物在一定的中间组成范围内，在机械损伤后进行显著的自主修复。如果这种无法解释的观察在分子水平上被理解，它可能会带来很高的科学和技术回报。该项目还将探索设计具有自我修复性能的新型共聚物，这将减少它们的消耗并对生态产生积极影响。这一新的基础知识可用于探索其他商品聚合物，同时以跨学科的方式培训学生，使他们做好应对全球技术挑战的准备。技术摘要：本项目旨在阐明商品聚(甲基丙烯酸甲酯/丙烯酸丁酯)p(MMA/NBA)共聚物惊人自愈的分子起源。这将通过精确合成45/55-55/45 MMA/NBA摩尔组成范围内的交替、随机和嵌段共聚物来实现，与自我愈合的程度相关，并确定支配这一独特行为的分子事件。为此，将采用原子转移自由基聚合(ATRP)和非均相自由基聚合(HRP)合成具有不同嵌段尺寸的窄分散共聚物。这些实验将允许确定邻近的MMA和NBA共聚重复单元在损伤修复周期和随后的自我修复过程中对构象变化的作用。还将研究在机械损伤过程中可能产生的自由基的作用，作为共聚物相对分子质量和共聚物拓扑结构的函数，特别是它们在再结合中的作用。由于链断裂和/或滑移预计与共聚物组成有关，因此将利用原位表面/界面化学成像(IR/拉曼)、电子顺磁共振(EPR)和核磁共振(核磁共振)光谱来识别与自愈有关的分子事件。如果在机械损伤过程中产生本征自由基，它们将作为动态核极化(DNP)剂选择性地增强损伤部位核的魔角旋转(MAS)核磁共振信号。这些测量将作为共聚物拓扑结构、相对分子质量和分散性的函数进行，并将提供有关聚合物链的特定原子级构象、自由基浓度水平和损伤位置的化学基团性质的信息。计划中的实验研究将与分子动力学模拟平行进行，分子动力学模拟将检验范德华和其他相互作用对共聚物拓扑结构和自愈行为的作用。

NON-TECHNICAL SUMMARY:Polymers exhibit a wealth of useful properties that make these materials uniquely applicable for a broad range of applications in all areas of technology and society. If commodity polymers were capable of self-repair upon fracture, many new applications could be sought out, enabling long-lasting properties, new functions, and substantial savings. This project seeks to understand the observed self-healing behavior in a type of commodity polymers (acrylate-based copolymers) which, in a certain intermediate compositional range undergo remarkable autonomous repair upon mechanical damage. If this unexplained observation is understood at a molecular level, it may offer high scientific and technological payoffs. This project will also explore the design of new copolymers with self-healing properties, which would reduce their consumption and have positive ecological impacts. This new fundamental knowledge may be used to explore other commodity polymers and at the same time train students in an interdisciplinary manner and prepare them to tackle global technological challenges.TECHNICAL SUMMARY:This project aims to elucidate molecular origins of a surprising self-healing in commodity poly(methyl methacrylate/n-butyl acrylate), p(MMA/nBA), copolymers. This will be pursued by precisely synthesizing alternating, random, and block copolymers in the 45/55 - 55/45 MMA/nBA molar compositional range, correlating with the extent of self-healing, and identifying molecular events that govern this unique behavior. For that purpose, narrow dispersity copolymers with variable block sizes will be synthesized using atom transfer radical polymerization (ATRP) and heterogeneous radical polymerization (HRP). These experiments will allow to determine the role of the neighboring MMA and nBA copolymer repeating units on conformational changes during the damage-repair cycle and subsequent self-repair. The role of free radicals which can be potentially generated during mechanical damage as a function of copolymer molecular weight and copolymer topologies, and particularly their role in rebonding, will also be investigated. Since chain cleavage and/or slippage are expected to be copolymer-composition dependent, to identify molecular events responsible for self-healing, in-situ surface/interfacial chemical imaging (IR/Raman), electron paramagnetic resonance (EPR), and nuclear magnetic resonance (NMR) spectroscopy will be utilized. If intrinsic free radicals are generated during mechanical damage, they will act as dynamic nuclear polarization (DNP) agents to selectively enhance the magic-angle spinning (MAS) NMR signals of nuclei at the damage site. These measurements will be conducted as a function of copolymer topology, molecular weight, and dispersity, and will provide information about specific atomic-level conformation of the polymer chains, concentration levels of free radicals, and the nature of chemical groups at the site of damage. The planned experimental studies will parallel molecular dynamics simulations which will examine the role of van der Waals and other interactions on copolymer topologies and self-healing behavior.