Cyclic Polymers: Topological Effects on Structure, Dynamics and Function

技术概述：大分子在现代技术中无处不在。 几十年来，环状大分子一直吸引着化学家、生物学家和材料科学家。 虽然线性大分子的性质是合理的理解，环状大分子的性质仍然是神秘的。 将大分子约束成环对大分子的结构、动力学和性能有着重要的影响。我们利用这些新特性来产生新材料类别的能力受到我们的理解和我们无法产生具有高纯度的明确结构的高分子量环状聚合物的限制。 发现了一种新颖的内酯的两性离子扩环聚合，其提供了具有明确分子量和窄分子量分布的高分子量环状聚酯的有利合成。 这种新的合成策略是快速的、可扩展的，并且使得能够产生跨越分子量的结晶环状聚酯，其中链缠结开始主导其性质。 我们的实验方法将聚合反应的机理研究与物理，流变学和光谱研究（宽角和小角X射线和中子散射）相结合，以阐明分子拓扑结构对大分子构象，动力学和性能的作用。 我们对线性大分子最简单的拓扑异构体之一的基本理解的差距是拟议研究的具体目标。 该实验计划旨在提供新的知识来填补这些空白，并将这些知识应用于开发新型高性能热塑性塑料，弹性体和智能流变液。虽然重点是环状聚酯，但所得出的基本见解应可推广到任何环状大分子，突出了拟议研究的更广泛的知识影响非技术摘要：塑料是无处不在的现代材料，影响着我们生活的方方面面。 大多数塑料都来自线性聚合物，长线性链大分子，其性质相当好理解。 相比之下，环状聚合物，大的大分子封闭成一个环，表现出不寻常的性质，完全不同于他们的线性类似物，但这些差异还没有得到很好的理解。 我们利用这些新特性来产生新材料类别的能力受到我们的理解和我们不能产生具有高纯度的明确结构的高分子量环状聚合物的限制。开发了一种新的合成技术，提供了一种生成环状聚酯的方法。 这种新的方法将使新类别的定义明确的环状聚合物的制备，以研究它们的性能和可能的应用，作为新类别的聚合物材料。 研究将解决环状聚合物如何结晶成硬热塑性塑料，它们在熔融时如何流动，以及它们的末端连接成环的简单事实如何改变它们的行为。 我们对环状聚合物知之甚少，这意味着我们对聚合物的理解远没有以前想象的那么复杂。 也就是说，如果连接一个大的线性分子的两端以无法解释的方式改变了它的性质，那么我们能说我们理解这些大分子吗？ 拟议研究的一个主要影响将是对环中限制的大分子行为的新的科学理解，以及这些新见解挑战和增强我们目前对大分子行为的理解的程度。 随着新的见解的出现，环状聚合物的新特性可以用来创造新的材料家族。 与IBM的工业科学家，NIST的物理科学家和斯坦福大学的化学工程师的合作努力将为下一代科学家提供独特的培训环境，他们能够制造新的材料类别，研究它们的特性并利用这些见解来生成新的聚合物材料类别。

TECHNICAL SUMMARY:Macromolecules are ubiquitous in modern technologies. Cyclic macromolecules have fascinated chemists, biologists and materials scientists for decades. While the properties of linear macromolecules are reasonably well understood, the properties of cyclic macromolecules remain mysterious. Constraining a large macromolecule into a ring has a significant influence its structure, dynamics and properties. Our ability to exploit these novel properties to generate new classes of materials is constrained both by our understanding and our inability to generate high molecular weight cyclic polymers with well defined structures in high purity. An innovative zwitterionic ring-expansion polymerization of lactones was discovered that provides an expedient synthesis of high molecular weight cyclic polyesters of well-defined molecular weight and narrow molecular weight distribution. This new synthetic strategy is fast, scalable and enables the generation of crystalline cyclic polyesters that span molecular weights where chain-entanglements begin to dominate their properties. Our experimental approach combines mechanistic studies of polymerization reactions with physical, rheological and spectroscopic investigations (wide- and small-angle X-ray and neutron scattering) to illuminate the role of molecular topology on macromolecular conformation, dynamics and properties. The gaps in our fundamental understanding of one of the simplest topological isomers of linear macromolecules are specific targets of the proposed studies. The experimental plan is designed to provide new knowledge to fill these gaps and to apply this knowledge for the development of new classes of high-performance thermoplastics, elastomers, and smart rheological fluids. While the focus is cyclic polyesters, the fundamental insights derived should be generalizable to any cyclic macromolecule, highlighting the broader intellectual impacts of the proposed studies NON-TECHNICAL SUMMARY: Plastics are ubiquitous modern materials, which impact every facet of our lives. Most plastics are derived from linear polymers, long linear chain macromolecules whose properties are reasonably well-understood. In contrast, cyclic polymers, large macromolecules closed into a ring exhibit unusual properties quite different from their linear analogs, but these differences are not well-understood. Our ability to exploit these novel properties to generate new classes of materials is limited both by our understanding and our inability to generate high molecular weight cyclic polymers with well defined structures in high purity. A new synthetic technique was developed that provides a means of generating cyclic polyesters. This new method will enable the preparation of new classes of well-defined cyclic polymers to investigate their properties and possible applications as new classes of polymeric materials. Studies will address how cyclic polymers crystallize into hard thermoplastics, how they flow when melted, and how the simple fact that their ends are connected into a ring changes their behavior. That so little is known about cyclic polymers implies that our understanding of polymers is far less sophisticated than previously imagined. That is, if connecting the ends of a large linear molecule changes its properties in ways that can't be explained, can it be said that we understand these large molecules? A major impact of the proposed studies will be new scientific understanding on the behavior of macromolecules constrained in rings and the degree to which these new insights challenge and augment our current understanding of macromolecular behavior. As new insights emerge, the novel properties of cyclic polymers can be harnessed to create new families of materials. Collaborative efforts with industrial scientists at IBM, physical scientists at NIST, and chemical engineers at Stanford will provide a unique training environment for the next generation of scientists who are able to make new classes of materials, study their properties and use these insights to generate new classes of polymeric materials.