Characterization of Polymers with the Kerr-Effect

技术概述：为了更全面地了解和改进聚合物材料的性能，必须建立详细的结构-性能关系，以确定改变聚合物的化学微结构对其行为的影响。这种结构-性质关系的建立需要测量具有不同微结构的聚合物的性质，而这些微结构需要仔细地表征。美国国家科学基金会最新的聚合物研讨会报告总结道：“聚合物合成的最新进展导致精细和精确的体系结构，这需要在现有技术之外的微结构表征方面取得相应的进展，而这些技术是共同不足的。”观察强电场稀释溶解在介电常数较低的非极性溶剂中的聚合物溶液所产生的双折射，即电双折射或克尔效应，可能提供一种比目前最灵敏的核磁共振光谱技术更全面地表征聚合物微结构的方法。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，在符号上可以是正的或负的。从聚合物的稀溶液中测量的MKS可能比核磁共振谱对其微观结构更敏感。由于聚合物的MK是其整个链的“宏观”性质特征，任何微观结构元素改变其整体极化率张量或改变其整体偶极矩向量相对于其最大极化率方向的大小和/或方向都将影响其MK。与核磁共振或其他仅依赖于局部聚合物微结构的光谱不同，沿着聚合物链(中端和末端)的微结构的宏观位置/位置也可能影响其MK或Kerr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：美国国家科学基金会最新的聚合物研讨会报告总结说，“聚合物合成的最新进展导致精细和精确的体系结构，需要在现有技术之外的微结构表征方面取得相应的进展，而这些技术是共同不足的。”在施加强电场稀释聚合物溶液时产生和观察到的光学特性的变化可以提供一种更好的手段来表征其组成的长链分子的微观结构，从而建立这些材料的改进的微结构-性能关系，以及它们在各种最终用途中的设计和最佳应用。除了研究生，本科生和高中生将帮助进行各种聚合物的基于光学特性的微结构表征。每年夏天，一名高中生将在美国化学学会的种子计划下接受指导，该计划旨在提供刺激的暑期研究经验，鼓励贫困和代表性不足的高中生进入大学，主修科学/技术领域。此外，在通过表征聚合物的微结构来改善聚合物的结构-性能关系方面取得的进展将在聚合物科学和工程研究生课程中介绍。

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.