Characterization of Polymers with the Kerr-Effect

技术概要：为了更全面地理解和改善聚合物材料的性能，必须开发详细的结构-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。 这种结构-性能关系的建立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被仔细表征。 最新的NSF研讨会关于聚合物的报告得出的结论是，“聚合物合成的最新进展导致了复杂和精确的结构，需要在微观结构表征方面伴随着超越目前可用技术的进展，而这些技术总体上是不够的”。 通过对溶解在具有低介电常数的非极性溶剂中的聚合物稀溶液施加强电场，电双折射或克尔效应，可以提供一种手段，更充分地表征聚合物微结构比可以实现与目前最敏感的技术，NMR光谱。 包括单体在内的小分子的摩尔克尔常数mKs的范围超过四个数量级，此外，其符号可以是正的或负的。 从聚合物的稀溶液中测量的聚合物的mK可以比NMR光谱对它们的微观结构更敏感。因为聚合物的mK是其整个链的“宏观”性质特征，所以任何改变其总体极化率张量或改变其总体偶极矩矢量相对于其最大极化率方向的大小和/或取向的微观结构元素都将影响其mK。与仅依赖于局部聚合物微结构的NMR或其它光谱不同，微结构沿聚合物链（中间对末端）的宏观位置/定位沿着也可影响其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/定位。 非技术性总结：最新的NSF研讨会关于聚合物的报告得出的结论是，“聚合物合成的最新进展导致了复杂和精确的结构，需要在微观结构表征方面伴随着超越目前可用技术的进展，而这些技术总体上是不够的”。通过对聚合物稀溶液施加强电场产生和观察到的光学特性的变化可以提供表征其组成长链分子的微观结构的上级手段，从而建立这些材料的改进的微观结构-性能关系以及它们的设计和各种最终用途的最佳应用。沿着研究生、本科生和高中生将协助进行各种聚合物的基于光学性质的微观结构表征。每年夏天，一名高中生将在美国化学学会的项目种子计划下接受指导，该计划旨在提供刺激的夏季研究经验，以鼓励贫困和代表性不足的高中生上大学并主修科学/技术领域。此外，通过表征其微观结构来改善聚合物结构-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.