Characterization of Polymers with the Kerr-Effect

技术概述：为了更全面地了解和提高聚合物材料的性能，必须发展详细的结构-性能关系，以确定改变聚合物的化学微观结构如何影响其行为。建立这种结构-性能关系需要测量具有不同微观结构的聚合物的性能，并且这些微观结构需要仔细表征。美国国家科学基金会关于聚合物的最新研讨会报告得出结论：“聚合物合成的最新进展导致了复杂而精确的结构，这需要在微观结构表征方面取得进展，而不是目前可用的技术，而这些技术总体上是不足的。”用强电场稀释溶解在低介电常数的非极性溶剂中的聚合物溶液所产生的双折射现象。与目前最灵敏的核磁共振波谱技术相比，电双折射或克尔效应可能提供一种更全面地表征聚合物微观结构的方法。包括单体在内的小分子的摩尔克尔常数（mk）的变化幅度超过4个数量级，此外，其符号可以是正的，也可以是负的。从聚合物的稀溶液中测量的分子量比核磁共振光谱对其微结构更敏感。由于聚合物的mK是其整个链的“宏观”性质特征，任何改变其整体极化张量或改变其整体偶极矩矢量相对于其最大极化率方向的大小和/或方向的微观结构元素都会影响其mK。聚合物链上微观结构的宏观位置/位置（中间或末端）也可能影响其mK或克尔效应，从而允许识别这种“精细和精确的聚合物结构”的位置/位置。非技术总结：最新的NSF研讨会关于聚合物的报告得出结论：“聚合物合成的最新进展导致了复杂和精确的结构，这需要在微观结构表征方面取得进展，而不是目前可用的技术，而这些技术总体上是不足的。”对聚合物的稀释溶液施加强电场所产生和观察到的光学特性的变化，可能为表征其组成长链分子的微观结构提供了一种优越的手段，从而为这些材料及其设计和各种最终用途的优化应用建立了改进的微观结构-性能关系。与研究生一起，本科生和高中生将协助进行各种聚合物的基于微观结构表征的光学性质。每年夏天，一名高中生将接受美国化学会SEED项目的指导，该项目旨在提供令人兴奋的暑期研究经历，以鼓励贫困和代表性不足的高中生上大学，主修科学/技术领域。此外，通过表征聚合物的微观结构来改善聚合物的结构-性能关系的进展将在研究生高分子科学与工程课程中介绍。

TECHNICAL SUMMARY: To more fully understand and improve the properties of polymer materials detailed structure-property relations must be developed to determine how changing the chemical microstructures of polymers effects their behaviors. Establishment of such structure-property relations requires measurement of the properties of polymers with different microstructures, and these micro-structures need to be carefully characterized. The latest NSF Workshop report on Polymers concluded that "recent advances in polymer syntheses leading to elaborate and precise architectures require accompanying advances in microstructural characterization beyond currently available techniques, which are collectively inadequate". Observation of the birefringence that is produced by application of a strong electric field to dilute solutions of polymers dissolved in non-polar solvents with low dielectric constants, ie., electrical birefringence or the Kerr-Effect, may provide a means to more fully characterize polymer microstructures than can be achieved with the currently most sensitive technique, NMR spectroscopy. Molar Kerr constants, mKs, of small molecules including monomers, range over more than four orders of magnitude, and, in addition, may be either positive or negative in sign. mKs of polymers measured from their dilute solutions can be more sensitive to their microstructures than NMR spectra. Because a polymer's mK is a "macroscopic" property characteristic of its entire chain, any microstructural element that alters its overall polarizability tensor or changes the magnitude and/or orientation of its overall dipole moment vector with respect to the direction of its maximum polarizability will effect its mK. Unlike NMR or other spectroscopies dependent only upon local polymer microstructures, the macroscopic positions/locations of microstructures along the polymer chain (middle vs. end) may also effect its mK or Kerr-Effect, thereby permitting identification of the positions/locations of such "elaborate and precise polymer architectures". NON-TECHNICAL SUMMARY : The latest NSF Workshop report on Polymers concluded that "recent advances in polymer syntheses leading to elaborate and precise architectures require accompanying advances in microstructural characterization beyond currently available techniques, which are collectively inadequate". The changes in optical characteristics produced by and observed upon application of a strong electric field to dilute solutions of polymers may provide a superior means to characterize the microstructures of their constituent long chain molecules leading to the establishment of improved microstructure-property relations for these materials and their design and optimal application to various end uses. Along with graduate students, undergraduate and high school students will assist in conducting the intended optical property based microstuctural characterizations of various polymers. Each summer a high school student will be mentored under the Project SEED program of the American Chemical Society, which seeks to provide a stimulating summer research experience to encourage underprivileged and underrepresented high school students to go to college and major in a science/technology field. In addition, advancements made in improving structure-property relations for polymers by characterizing their microstructures will be introduced in graduate Polymer Science and Engineering courses.