NMR studies of fluoropolymers and of polyaniline

Abstract

This thesis presents a study of two polymers, poly(trifluoroethylene) (PTrFE) and polyaniline (PANi), by means of Nuclear Magnetic Resonance Spectroscopy (NMR).The first part of the thesis focusses on investigations in connection with the fluoro polymer. Using known assignments of the fluorine solution-state spectrum the defect level could be determined as well as a high degree if atacticity confirmed. Solid-state NMR concentrated, on the one hand, on the detection of heterogeneities in the polymer and, on the other hand, on the investigation of cross-polarisation dynamics of abundant spin systems, namely (^1)→(^13)C CP. To account for the two different kinds of fluorine in PTrFE a three-spin-bath model based on the usual spin- temperature approach has been developed, numerically investigated and applied to PTrFE. The success, however, was limited by the influence of coherent polarisation transfer in the early stage of the CP. The transient oscillations in (^1)→(^13)C CP curves have been used in order to determine bond distances and, subsequently, to detect motion of the polymer chain. The onset of motion has been confirmed by comparing the measured axially symmetric fluorine shielding anisotropy tensor with the asymmetric tensor obtained from ab initio calculations carried out on the rigid molecule. The second part is concerned with NMR of polyaniline with emphasis on proton wideline NMR of leucoemeraldine. Spin-lattice relaxation data inferred heterogeneity in the powder polymer with a fast relaxing component of about 5% intensity. Impurities as a source of this heterogeneity as well as partial crystallinity have been excluded on the basis of solution-state NMR results and X-ray results, respectively. Furthermore, proton spin-diffusion experiments suggest that the domains having different relaxation characteristics are in close contact, although no definite particle size has been determined. Experiments at elevated temperatures show an increase of the intensity of the fast relaxing component. A reversible transformation of regions with inherent motional heterogeneity has been inferred.