| Liquid crystalline polymers were studied with Nuclear Magnetic Resonance (NMR) techniques. Solution, solid state and microimaging NMR were employed to investigate isotropic and anisotropic phase changes, polymer chain alignment in the anisotropic phases and inter-, intra-phase molecular diffusion. New NMR methods for the study of liquid crystalline phase were developed and instruments were built to fulfill the implementation of these experiments.; Natural abundance 13C and 1H NMR was first used successfully to study phase transitions of lyotropic polyamides in sulfuric acid solutions and thermotropic polyester melts as a function of temperature, concentration, and changes in molecular structure. Order parameter information for rigid polyamide chains in the anisotropic phase were extracted through spectral simulation and with the aid of solid state chemical shift tensor measurements. This NMR spectral simulation method has the advantage over light and electric measurements that it can distinguish the behaviors from coexisting isotropic and anisotropic phases, while not requiring synthetic isotope enrichment. Order parameter changes were then observed and they are discussed on the basis of thermal and athermal theories describing the liquid crystalline behavior. During the course of this work a new method of determining anisotropic 13C chemical shift displacements was also developed based on correlating anisotropic chemical shifts to isotropic ones through mechanical polymer director reorientations. Molecular diffusion coefficients of liquid crystalline phases were also obtained successfully by the employment of pulsed-gradient spin-echo (PGSE) experiments, probing 13C nuclei with 1H decoupling. |
