Characterization of Polymers with the Kerr-Effect

North Carolina State University, Raleigh NC

Investigators

Abstract

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.