The friction and wear behavior of three thin polyimide films of known chemical structure was tested. An attempt was made to correlate differences in chemical structure, primarily the presence of flexible linkages and highly polar side groups, to differences in tribological properties. The wear test results showed lowest wear for the polyimide with the flexible oxygen linkage. The wear mechanism was deduced to be fatigue since wear did not occur immediately and a strong correlation was noted between wear rate and elastic modulus. Increasing sliding speed increased both wear rate and friction coefficient. The friction results showed highest friction for the polyimide with the highest density of polar side groups. Even though some effects of the deformation component of friction were seen, the adhesive component of friction predominated. / Master of Science

The modification of polyimide films by tin-complex incorporation has been studied with the aim of producing materials with the mechanical and thermal properties of polyimide with enhanced electrical properties. A variety of Sn(II) and Sn(IV) complexes have been incorporated into BTDA/ODA (3,3 14,4 1-benzophenonetetracarboxylic acid dianhydride / 4,41- oxydianiline) and PMDA/ODA (pyromellitic dianhydride/4,4 1 -oxydianiline) derived polyimides in a 1:4 (complex/polymer repeat unit) molar ratio. Tin-complex incorporation was seen to have a variety of effects upon polyimide properties, depending upon the particular tin-complex employed. All films produced were thermally stable with decomposition temperatures> 500°C. Most films were homogeneous and flexible. / Master of Science

A series of reactive phenylethynyl endcapped imide oligomers has been prepared in either fully cyclized or amic acid precursor form. Soluble oligomers have been synthesized with controlled molecular weights ranging from 2- to 12 Kg/mol. Molecular weight characterization was performed using SEC (size exclusion chromatography) and 13C-NMR, revealing good agreement between the theoretical and experimental (Mn) values. Crosslinked polyimides were obtained by solution or melt processing the oligomers into films and gradually heating in a programmed temperature manner up to the appropriate reaction temperature for the phenylethynyl groups, which is approximately 350-400°C. Thermal analysis of the resulting films showed high glass transition temperatures (>300°C) and excellent thermal stability, comparable to those found for thermoplastic control polyimides. The crosslinked films also had exceptional solvent resistance as evidenced by a high gel fraction (greater than or equal to 95%) following extraction in common solvents for several days. This was in contrast to the amorphous thermoplastic controls, which quickly dissolved upon immersion in solvents. The monomers used for synthesizing the polyimide oligomers were varied systematically within the series to study the influence of both molecular structure and molecular weight on the physical and film-forming properties. The incorporation of fluorinated monomers, such as 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), reduced water absorption and lowered the dielectric constant relative to non-fluorinated polyimides in the series. When flexible ether linkages were incorporated in the repeat unit by using 4,4'-oxydianiline (ODA), relatively more ductile solvent-cast films were obtained from oligomers having Mn values as low as 10 Kg/mol. Additionally, oligomer Mn and the relative rigidity/symmetry of the repeat unit structure greatly influenced the solubility of polyimides in NMP. For example, even 6FDA/p-phenylenediamine based oligomers with Mn values targeted below 10 Kg/mol precipitated from NMP at 180°C during solution imidization. The relationship between solution viscosities of polyimide and poly(amic acid) thermosetting oligomers and wetting/spreading ability to form continuous films during spin casting was elucidated. Employing o-dimethoxybenzene (DMB) as a cosolvent with NMP improved the film-forming ability of the fully imidized 6FDA/ODA oligomer series. This was evidenced by a decrease in viscosity (via suppression of physical-type gel formation) and better overall coverage and clarity of the films. Humidity was found to have a detrimental effect, causing the polyimide oligomers to phase separate to form cloudy or porous films. When moisture was reduced, oligomers having Mn greater than or equal to 6 Kg/mol formed spin cast films of <20 micrometer thickness with good qualitative adhesion to several inorganic substrates. Dielectric constants (epsilon) were estimated for several of the polyimides by measuring the refractive indices (n) of the films and using Maxwell's relationship (epsilon at optical frequencies is equal to n raised to the second power). The apparent dielectric constants were low, ranging from 2.47 to 2.75. The novel combination of low dielectric constant, solvent resistance and isotropic physical properties inherent in the thermosetting polyimide oligomers makes these materials excellent candidates for use as thin film insulating layers in microelectronics packaging applications. / Ph. D.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

Thesis (Honors)--College of William and Mary, 2009. / Includes bibliographical references (leaf 36). Also available via the World Wide Web.

Thesis (Ph. D.)--University of Hong Kong, 2002. / Includes bibliographical references (leaves 219-222).

No description available.

Thesis(M.S.)--Auburn University, 2007. / Abstract. Vita. Includes bibliographic references (p.44-45).

Thesis (Ph. D. in Interdisciplinary Materials Sciences)--Vanderbilt University, Dec. 2008. / Title from title screen. Includes bibliographical references.

Dissertation (Ph.D.)--University of Toledo, 2005. / Typescript. "As partial fulfillment of the requirements for the Doctor of Philosophy Degree in Engineering."