Date Awarded


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)




The motivation for this study was to further characterize a relatively new high-temperature polymer for application as a matrix resin for carbon fiber composites. The two primary questions addressed in this study dealt with the structural and chemical changes occurring in these polymers on exposure to high temperature.;To investigate the structural changes in the heat-treated samples, a positron annihilation lifetime spectrometer was designed, built and optimized. Because the lifetime of a positron in a material reflects the electronic structure of the material in which it annihilates, measurements by positron annihilation lifetime spectroscopy can be used to investigate changes in a material at the Angstrom level. The results of applying this technique indicate that positron annihilation lifetime spectroscopy is able to detect microstructural changes in these heat-treated polymers.;In order to study the chemical changes occurring in these polymers during heat treatment, an array of solid state analytical techniques was applied. These techniques included Differential Scanning Calorimetry, Elemental Analysis, Thermo-gravimetric and Thermo-mechanical analyses, Fourier Transform Infrared, {dollar}\sp{lcub}13{rcub}{dollar}C Cross Polarization Nuclear Magnetic Resonance, Electron Spin Resonance, and Dynamic Nuclear Polarization. The results of applying these techniques provide previously unavailable data into the chemical structures of these polymers before and after heat treatment. Additionally, the presence of stable free radicals in the polymer samples both before and after heat treatment was confirmed and the origin and location of these free radicals is proposed.



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