RUI: Dynamic Guanidine-based Polymer Networks

第1部分：非技术性材料一般可分为两类：(A)热塑性塑料，如塑料瓶、食品袋和尼龙，加热后变软，可重新模塑和回收；(B)热固性材料，如轮胎、环氧胶和树脂，具有永久性形状，非常难再加工。因此，热固性塑料的再利用潜力有限，最终会通过资源消耗和大量废物的积累对环境产生负面影响。在分子水平上，这两类材料之间的差异源于这样一个事实，即热塑性塑料由离散的聚合物链组成，这些聚合物链在受热时可以移动和流动，而热固性塑料是由永久粘合在一起的交联分子网络构建的。为了弥合这些材料之间的差距，最近的努力集中在使它们的固定网络可逆--也就是说，使它们能够在一定条件下解除交联，然后对网络进行改革，允许热固性材料重塑和再加工。这些系统代表了一种被称为动态聚合物网络的新材料类别。虽然动态聚合物网络在过去20年里一直是相当多研究的焦点，但关于它们的许多基本问题仍然存在，削弱了它们的实用价值，并限制了它们在研究实验室以外的应用。这项研究将利用一种旨在解交联热固性树脂的新型化学反应的独特特性，以全面了解动态聚合物网络的基本原理。PI研究目标的成功实现将产生各种可再加工的热固性材料，并将特定的分子级特性与宏观特性联系起来，有助于塑造这些先进材料在可持续制造、先进医学和下一代电池等领域的未来设计和应用。参与这项研究的学生将接受跨学科的培训，涉及合成化学、聚合物表征和各种性能测定技术。第2部分：技术摘要动态聚合物网络是一种共价交联材料，将热固性树脂的理想性能与热塑性塑料的可再加工性结合在一起。它们的交联链经历可逆的交换反应，在特定条件下被激活，不断地重组网络。最近，PI展示了一种基于先前未知的胍类交换反应的新型材料。这项提议旨在利用动态的基于胍的聚合物网络的独特能力来回答动态材料领域的基本问题，并扩大这些系统可实现的性质的窗口。这项建议的具体目标是：(1)利用胍官能团的多功能性来修饰其反应性并引入非共价键伙伴，从而建立基本分子尺度性质与宏观流变行为之间的联系；以及(2)在各种精确改变的聚合物结构中引入金刚烷交联物，以阐明“背景”聚合物的特定特征在决定动态网络行为中的作用。这些研究将由学生研究人员使用合成技术、聚合物表征、流变学分析和介电光谱学相结合来完成。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

PART 1: NON-TECHNICAL SUMMARYPolymeric materials can generally be divided into two categories: (a) thermoplastics, materials such as plastic bottles, grocery bags, and nylon, that soften with heat and can be remolded and recycled; and (b) thermosets, those such as tires, epoxy adhesives, and resins, that have a permanent shape and are very difficult to reprocess. Thermosets thus have limited potential for reuse, ultimately having a negative impact on the environment through resource consumption and accumulation of large amounts of waste material. At the molecular level, the difference between these two classes of materials arises from the fact that thermoplastics consist of discrete polymer chains that can move and flow when heated, whereas thermosets are built from a crosslinked molecular network that is permanently bonded together. To bridge the gap between these materials, recent efforts have focused on making their fixed networks reversible -- that is, enabling them to de-crosslink under certain conditions followed by reformation of the network, allowing thermosets to be remolded and reprocessed. These systems represent a new class of materials known as dynamic polymer networks. While dynamic polymer networks have been the focus of considerable research during the last two decades, many fundamental questions about them remain, detracting from their practical utility and restricting their applications beyond the research lab. This research will leverage the unique characteristics of a novel chemical reaction aimed at de-crosslinking thermosets in order to gain generalized insight into the fundamental principles of dynamic polymer networks. Successful realization of the PI’s research goals will yield a wide variety of reprocessable thermosets and link specific molecular-level characteristics with macroscopic properties, helping to shape future designs and applications of these advanced materials in areas as varied as sustainable manufacturing, advanced medicine, and next-generation batteries. Students participating in this research will be trained in an interdisciplinary manner involving synthetic chemistry, polymer characterization, and a variety of techniques for property determination.PART 2: TECHNICAL SUMMARYDynamic polymer networks are covalently crosslinked materials that combine the desirable properties of thermosets with the reprocessability of thermoplastics. Their crosslinks undergo reversible exchange reactions that are activated under specific conditions, continuously reorganizing the network. Recently the PI demonstrated a new type of these materials based on previously unknown exchange reactions of guanidines. This proposal seeks to leverage the unique capabilities of dynamic guanidine-based polymer networks to answer fundamental questions in the field of dynamic materials and expand the window of achievable properties of these systems. Specific objectives of this proposal are to: (1) use the versatility of the guanidine functionality to both modify its reactivity and introduce noncovalent bonding partners, establishing the link between fundamental molecular-scale properties and macroscopic rheological behavior; and (2) incorporate guanidine crosslinks into a variety of precisely altered polymer structures to elucidate the role of specific characteristics of the “background” polymer in determining the behavior of dynamic networks. These studies will be accomplished by student researchers using a combination of synthetic techniques, polymer characterization, rheological analysis, and dielectric spectroscopy..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.