Precise Copolymers and Ionomers: Conductivity in Layered and Percolated Morphologies and Mechanical Properties

聚乙烯在现代生活中无处不在，从塑料袋到牛奶罐再到煤气管。 通过将酸和离子基团连接到分子上来改性聚乙烯，将聚乙烯转变为具有更好的耐化学性的显著更坚韧和更耐磨的材料。 这些改进的性质源于含有酸基和金属离子的纳米级聚集体的存在。这些离子聚集体一直被认为是球形的，聚合物科学家知道如何操纵这种结构来调节机械性能。在这项研究中，PI计划设计这些纳米级聚集体来促进离子或质子传输。 具有快速和高选择性离子或质子传输的新型塑料将有助于水处理，能量储存和能量转换的突破。宾夕法尼亚大学的Karen Winey沿着和她的研究生及本科生一直在研究精确的聚乙烯，其中酸或离子基团沿沿着分子链均匀分布。 他们发现，这些精确的共聚物表现出新的，但尚未测试的离子聚集体类型。 通过选择不同的聚合物和离子，离子聚集体可以从球形纳米聚集体转变为片状和网状聚集体。 这两种新的结构是特别有前途的离子传输，因为聚集体比离散的球形聚集体更广泛。 该奖项将探索这些新型离子聚集体所提供的特性，旨在确定具有显著改善的离子或质子传输的聚合物。 聚合物合成和准弹性中子散射实验将使用国家facilities.Part 2：Technical SummaryPoly（ethylene-co-acrylic acid）precise copolymers是具有线性主链和侧链羧酸基团的模型聚合物，这些基团被精确地9、15或21个碳原子分开。这些精确的酸共聚物和它们的中和离聚物的先前形态学研究已经确定了各种聚集体形状，其中两种形态在导电性方面特别有趣。层状形态由组装成平面聚集体的官能团组成，并且层状形态具有横跨样品以形成共连续结构的线状、支链聚集体。相对于具有球形聚集体的单离子导体，层状和非层状聚集体具有更大的连接性，预期提供更快的离子传输。 离子电导率将在精确的酸共聚物与锂，钠，或铯中和研究。本文研究了水合精密酸共聚物和与各种咪唑类化合物混合的精密酸共聚物的质子导电性。这些精确的共聚物和离聚物提供了前所未有的分子控制，产生了明确的形态，从而促进了对离子和质子传输的结构-性能关系的更好理解。通过比较不同形貌类型的电导率，该项目将提供设计规则，使特定的形貌类型具有更好的导电性。一系列的实验方法将被应用于探测这些材料的结构，动力学和导电性，包括电化学阻抗谱，准弹性中子散射（QENS），介电弛豫谱，X射线散射，DSC，FTIR，NMR和机械性能。QENS结果与原子分子动力学模拟的直接比较将阐明内的导电机制的聚合物和探索离子运动是否从链动力学解耦。

PART 1: NON-TECHNICAL SUMMARYPolyethylene is ubiquitous in modern life from plastic bags to milk jugs to gas pipes. Modifying polyethylene by attaching acid and ionic groups to the molecule transforms polyethylene into a substantially tougher and more abrasion resistant material with better chemical resistance. These improved properties stem from the presence of nanoscale aggregates that contain the acid group and metal ions. These ionic aggregates have long been thought to be spherical, and polymer scientists know how to manipulate this structure to tune mechanical properties.In this research, the PI plans to engineer these nanoscale aggregates to promote ion or proton transport. New plastics with fast and highly selective ion or proton transport will contribute to breakthroughs in water treatment, energy storage, and energy conversion. Prof. Karen Winey along with her graduate and undergraduate students at the University of Pennsylvania have been studying precise polyethylenes where the acid or ionic groups are evenly spaced along the molecular chains. They found that these precise copolymers exhibit new, and as yet untested, types of ionic aggregates. By selecting different polymers and ions, the ionic aggregates can be transformed from spherical nanoscale aggregates to aggregates in the shape of sheets and percolated networks. Both of these new structures are particularly promising for ion transport, because the aggregates are more extensive than discreet spherical aggregates. This award will explore the properties afforded by these new types of ionic aggregates with the intent of identifying polymers with substantially improved ion or proton transport. Polymer synthesis and quasi-elastic neutron scattering experiments will use national facilities.PART 2: TECHNICAL SUMMARYPoly(ethylene-co-acrylic acid) precise copolymers are model polymers with a linear backbone and pendant carboxylic acid groups separated by exactly 9, 15 or 21 carbons. Previous morphology studies of these precise acid copolymers and their neutralized ionomers have identified a variety of aggregate shapes of which two morphologies are particularly interesting with respect to conductivity. The layered morphologies consist of functional groups assembled into planar aggregates and the percolated morphologies have stringy, branched aggregates that span the sample to make a co-continuous structure. Relative to single-ion conductors with spherical aggregates, the layered and percolated aggregates possess greater connectivity that is expected to provide faster ion transport. Ion conductivity will be studied in precise acid copolymers neutralized with Li, Na, or Cs. Proton conductivity will be studied in hydrated precise acid copolymers and precise acid copolymers mixed with various imidazoles. These precise copolymers and ionomers provide unprecedented molecular control that produces well-defined morphologies and thereby facilitate the improved understanding of structure-property relationships pertaining to ion and proton transport. By comparing conductivities for different morphology types, the proposed project will provide design rules for making specific morphology types with improved conductivity.An array of experimental methods will be applied to probe the structure, dynamics and conductivity of these materials including electrochemical impedance spectroscopy, quasielastic neutron scattering (QENS), dielectric relaxation spectroscopy, X-ray scattering, DSC, FTIR, NMR and mechanical properties. Direct comparison of the QENS results with atomistic molecular dynamics simulations will elucidate the mechanism of conduction within the percolated aggregates and explore whether or not the ion motion is decoupled from the chain dynamics.