Materials from High Molecular Weight Cyclic Polymers: Insights on Properties and Dynamics

聚合物无处不在；这些材料由长链分子构成，包括所有现代塑料、纺织品纤维以及包括蛋白质和DNA在内的生物学关键分子。该项目将利用一种新的方法来创建大型环状聚合物，以了解如何将长分子连接成一个环，影响由这些环状结构产生的材料的性质。环状聚合物与线性聚合物的不同之处在于只有一个单键，但这种微小的化学变化影响了这些分子在加工过程中的流动方式，它们如何固化以及它们如何与环境相互作用，这些方式仍然知之甚少。计划中的研究有三个具体目标。第一个目标侧重于产生由交联分子网络中的环聚合物衍生的新型材料，以研究这种纠缠环链如何影响材料的性质。第二个目标是阐明环状分子是如何流动的，从而更好地理解环状分子是如何相互缠绕以及与线性链分子缠绕的。第三个目标集中在循环结构对这些大分子在液体和固体状态下采用的形状的影响。该项目将支持和培养两名研究生，他们将有机会与来自国外和美国国家实验室的顶尖专家合作。首席研究员和研究生将参与当地学校的外展项目，以促进整个社区对科学的理解。技术概述本研究的重点是研究大环聚合物的构象、性质和应用，利用以前在生成大环链的新合成方法中的进展。两性离子开环聚合（ZROP）通过产生带有正电和负电的传播链来产生大的环状分子。用这种方法合成的三类聚合物将用于实现上述目标。水溶性环聚磷酸酯将被包裹在三维交联的水凝胶网络中，以研究包裹的环链如何影响所得双网络水凝胶的性质。这些新型材料预计将表现出相对于缺乏包裹链的凝胶增强的韧性。高分子量环碳硅氧烷聚合物的流变行为将被研究，以阐明环分子是如何纠缠的。这些材料的长度大约是相应线性链的纠缠分子量（Me）的125倍，这是以前任何其他合成方法都无法达到的分子量。这些研究的目的是调查是否大循环链可以表现出平台模量，是典型的线性链行为。将进行氘化高分子量环聚己内酯的中子散射实验，以验证环链浓缩溶液将呈现塌陷构象的理论预测。该项目的跨学科性质将为在聚合物合成方面受过训练的学生提供一个特殊的教育环境，使他们能够与世界上在聚合物流变学、聚合物物理学、中子散射和现代色谱分离方面的专家进行交流。

NON-TECHNICAL SUMMARYPolymers are ubiquitous; these materials, made of long-chain molecules comprise all modern plastics, the fibers of textiles, and the key molecules of biology including proteins and DNA. This project will leverage a new method for creating large cyclic polymers to learn how connecting a long molecule into a ring influences the properties of materials generated from these cyclic structures. Cyclic polymers differ from linear polymers by just a single bond, but this minor chemical change influences how these molecules flow during processing, how they solidify and how they interact with their environment in ways that remain poorly understood. The planned research targets three specific aims. The first aim focuses on the generation of new classes of materials derived from cyclic polymers entrapped in cross-linked molecular networks to investigate how such an entangled cyclic chain influences the properties of the material. The second aim seeks to illuminate how cyclic molecules flow to gain a better understanding of how ring-like molecules entangle with one another and with linear chain molecules. The third aim focuses on the influence of a cyclic structure on the shapes that these large molecules adopt in the liquid and solid states. This project will suport and educate two graduate students, who will have the opportunity to collaborate with leading experts from foreign countries and at US National Labs. The Principal Investigator and the graduate students will engage in outreach programs at local schools to promote increased scientific understanding in the community at large. TECHNICAL SUMMARYThis research focuses on investigations of the conformation, properties, and applications of large cyclic polymers by leveraging previous advances in a new synthetic method for generating large cyclic chains. Zwitterionic ring opening polymerization (ZROP) produces large cyclic molecules by generating propagating chains that contain both a positively-charged end and a propagating negatively charged chain end. Three classes of polymers synthesized with this method will be used to achieve the above-stated goals. Water-soluble cyclic polyphosphoesters will be entrapped in three-dimensional, cross-linked hydrogel networks to investigate how the entrapped cyclic chains influence the properties of the resultant double-network hydrogels. These novel materials are anticipated to exhibit enhanced toughness relative to gels lacking the entrapped chains. The rheological behavior of high molecular-weight cyclic carbosiloxane polymers will be investigated to illuminate how cyclic molecules entangle. These materials are of a length approximately 125 times the entanglement molecular weight (Me) of the corresponding linear chains -- a molecular weight regime previously unattainable by any other synthetic method. These studies are aimed at investigating whether large cyclic chains can exhibit a plateau modulus that is typical of linear chain behavior. Neutron-scattering experiments of deuteriated high molecular weight cyclic polycaprolactones will be carried out to validate theoretical predictions that concentrated solutions of cyclic chains will exhibit collapsed conformations. The interdisciplinary nature of this project will provide an exceptional educational environment for students trained in polymer synthesis to interact with world experts in polymer rheology, polymer physics, neutron scattering, and modern chromatographic separations.