Results are presented for two unrelated studies. The primary topic involved the crystallization behavior and morphological features of two polyimides, namely LARCCPI (Langley Research .Center Crystalline folyimide) and LARC-TPI (Thermoplastic folyimide). The LARC-CPI study first considered feature~ affecting crystallization behavior including inherent viscosity, crystallization temperature, and melt temperature and time. Data were analyzed using the A vrami analysis. Morphological features were investigated using techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), and small angle x-ray scattering (SAXS). Permanganic etching combined with SEM successfully revealed morphological detail, further supported by TEM data. These data support the Avrami analysis results. SAXS data reflected the influence of several crystalliz.ation variables on the long spacing. SAXS results also revealed the presence of a broad second scattering peak for semicrystalline samples appearing in the same position regardless of crystalliz.ation temperature or inherent viscosity. Molecular modelling predicted a low-energy helical conformation with a near-periodic repeat distance corresponding to the second SAXS peak. This conformation is offered as a tentative explanation for that peak. Finally, the effe.ct of nucleating agent on the recrystalliz.ability of a higher inherent viscosity LARC-CPI was considered. One of several nucleators appeared effective in enhancing recrystallization. The LARC-TPI study involved the development of a thermal cycle based upon crystalliz.ation kinetics results, allowing the successful recrystallization of LARC-TPI following exposure to elevated temperatures. This cycle was then used to modify an existing composite fabrication process to produce semicrystalline composites. Two carbon fiber types were utilized to make composites via both fabrication cycles. These composites were evaluated using several techniques. The second unrelated project examined very localized orientation behavior in two types of semi crystalline superstructure using FTIR microspectroscopy. Results were obtained utilizing linear dichroism for orientation within spherulitic and transcrystalline superstructure in poly(glycolide co-lactide) and isotactic polypropylene. An increase in orientation on an absolute basis as a function of position was successfully measured. Orientation function values were higher on an absolute basis for the transcrystalline superstructure. However, the sign of the isotactic polypropylene spherulite orientation function values was the opposite of what was anticipated. These results were considered in light of spherulite W AXS data also obtained. / Ph. D.

Earlier research relating to the use of polyimides modified with metal-ion complexes and metal particles indicate that enhanced conductivity and adhesive strength can be achieved. This research evaluated the employment of metal-modified polyimides to achieve optimum conductance at an aluminum joint. Condensation and addition polyimides were employed. The modification of the polyimides occurred in two ways. The first method involved homogeneous doping of the condensation polyimides with metal-ion complexes. The second modification method involved heterogeneous doping of condensation or addition polyimides with particles of a nickel-aluminum alloy. / Master of Science

LaRC-TPI, an aromatic thermoplastic polyimide, and Kapton®, a poly(pyromellitimide) were exposed to oxygen, argon and ammonia plasmas as pretreatments for adhesive bonding. Chemical changes which occurred in the surface as a result of the plasma treatments were investigated using x-ray photoelectron spectroscopy (XPS) and infrared reflection-absorption spectroscopy (IR-RAS). Water contact angle analysis was utilized to characterize the changes in surface wettability, and the ablative effects of the plasmas were monitored using ellipsometry and high resolution scanning electron microscopy (HR-SEM). Both XPS and IR-RAS results revealed the formation of polar functional groups at the surface. Contact angle analysis showed enhanced water wettability of the plasma-treated surfaces. As monitored by ellipsometry, oxygen and argon plasmas were seen to be highly ablative, whereas an ammonia plasma was only moderately so. HR-SEM micrographs revealed texturized surfaces in the case of oxygen and argon plasmas, but not in the case of ammonia plasma. Oxygen and argon plasmas appear to react with the polyimides via a fragmentation/oxidation mechanism, forming a loosely attached layer composed of low molecular weight polymer chains. The effect of ammonia plasma is postulated to be imide ring-opening resulting in the formation of amide functional groups. The 180° peel test was utilized to determine the receptability of the plasma-treated polyimide surfaces toward bonding with other polymeric materials. Adhesives used were a pressure sensitive acrylate and poly(ether sulfone). The pressure sensitive adhesive, although not representing a realistic bonding situation, does represent a system which presents the least disturbance to the plasma-modified layer, allowing the physical nature of the plasma-treated surface to be probed. The peel test values of the pressure sensitive adhesive/plasma-treated polyimide systems fell below the level of the non-treated controls, regardless of the plasma treatment used. Peel surface analysis revealed the presence of polyimide on the pressure sensitive adhesive failure surface, indicating failure in the plane of a weak boundary layer created by plasma. The removal of the weak boundary layer by solvent treatment restored the peel values to the level of the controls. Bonding of Kapton® films with poly(ether sulfone) showed an opposite trend; peel strengths of the plasma-treated samples all showed improvements versus the non plasma-treated control. Plasma treatments of LaRC-TPI which had been deliberately contaminated with mold release and high density polyethylene illustrated showed that plasma treatments are not always detrimental to adhesion. It was shown that the physical as well as the chemical nature of a polymer surface is critical to the level of adhesion which can be achieved. / Master of Science

Novel, high molecular weight, high glass transition temperature, photocrosslinkable polyimide and poly(imide siloxane) homo- and segmented copolymers were prepared and characterized. The polyimides were synthesized by the classical two step method of first preparing soluble poly(amic acid) prepolymers by the reaction of various aromatic dianhydrides with aromatic diamines. The siloxane modified copolymers were synthesized by reacting single or mixed components of the aromatic dianhydrides with a mixture of aromatic amine and bis(3-aminopropyl) end blocked polydimethyl siloxane oligomers in a cosolvent system of tetrahydrofuran and N-methyl-2-pyrrolidinone. These dysfunctional aminopropyl terminated siloxane oligomers were prepared through an anionic ring opening equilibration polymerization of octamethylcyclotetrasiloxane with bis(3—aminopropyl) tetramethyldisiloxane in the presence of siloxanolate catalyst. Soluble fully imidized polyimides were obtained by use of a solution imidization procedure which utilized a cosolvent system of N-methyl-2-pyrrolidinone and N-cyclohexyl-2-pyrrolidone at temperatures of approximately 170°C. The fully imidized polyimides were soluble in a variety of solvents. The homo- and copolymers have been characterized for compositional analysis by FT-IR and proton NMR spectroscopy. All polymers were characterized for their thermal properties by differential scanning calorimetry, dynamic mechanical thermal analysis and thermogravimetric analysis. All homoand copolymers possessed excellent thermal characteristics and good mechanical properties. The photosensitive properties of the polyimide and poly(imide siloxane) homo- and copolymers were investigated at the UV wavelengths of 313nm and 365nm. The photosensitivities were found to depend on both the amount of benzylic methyl substituted diamine incorporated into the polyimide backbone, and the amount of aromatic ketone concentration. High concentrations of fluorinated (6F) dianhydride were also desirable. Incorporation of the polydimethylsiloxane segments into the polyimide decreased the optical density without decreasing the photosensitivity and therefore desirably allowed thicker films to be crosslinked at lower exposure doses. The adhesion of the siloxane modified polyimides to the silicon wafers was increased with significantly increasing siloxane content and at 20 weight percent, eliminated the need for conventional coupling agents. / Ph. D.

Series of homo- and copolyimides containing controlled degrees of sulfonic acid ion conducting pendant groups have been synthesized from both phthalic (five-) and naphthalic (six-membered) dianhydrides and appropriate wholly aromatic diamines and heterocyclic analogues. The goal is to identify thermally and hydrolytically stable ion conducting polymers (ICP) suitable as proton exchange membranes, PEM, for fuel cells. The candidate ICP's have been synthesized and characterized for molecular weight, chemical composition, film forming properties, thermal transition behavior, boiling water stability, solvent solubility and water absorption and conductivity. Commercially available five-membered ring dianhydrides such as 6FDA, BPDA, and six-membered ring dianhydrides such as naphthalene tetracarboxylic dianhydride (NDA) have been used. High molecular weight five-membered ring polyimides were obtained from an equimolar ratio of diamines and dianhydride using a one-pot ester-acid procedure by initially converting the dianhydride to a diester-diacid derivative, followed by the reaction with sulfonated and unsulfonated aryl diamines. The sulfonated diamine monomer was allowed to oligomerize with the diester-diacid of the dianhydride for 2-3 hours, before unsulfonated diamine was charged into the reaction flask. The levels of sulfonation in the polymer backbones were controlled by varying the mole ratio of sulfonated diamine to unsulfonated diamine. For the six-membered ring polyimides, phenolic solvents, e.g. m-cresol, have been used. In general, 4,4′-diamino-biphenyl-2,2′-disulfonic acid (DPS) has been employed as the source of the sulfonated unit. The chemical compositions of both sulfonated and unsulfonated polyimides were obtained using ¹H-NMR and FT-IR. The sulfonic acid contents in both diamine monomers, as well as the sulfonated polyimides were also analyzed by acid-base potentiometric titration. In all cases, high inherent viscosity values and good film forming ability of the polymers were the key indications of high molecular weight. The viscosity values increased with an increase of sulfonation degree in the polymers. This increase of viscosity in these ionomers can be attributed to the increase of polymer chain aggregation with their increasing ionic character. Polymers were fabricated into membranes via solution casting or spin casting from DMAc or m-cresol in order to study film-forming properties. The solution cast dry films of the sulfonated polyimide membranes gave tough, ductile membranes and demonstrated moderate to high water absorption, which is necessary for PEM fuel cells. However, swollen films, in general, showed poor hydrolytic stability which resulted in brittle membranes. The solution-cast membranes were thermally analyzed to study the effect of the degree of sulfonation on the thermal properties of sulfonated polymers. All the thermograms of the sulfonated polyimide films exhibited a two-step degradation behavior. The first weight loss, observed between 300-400 °C, corresponds to desulfonation in the sulfonated block, and the second weight loss, observed for a temperature around 500 °C or above, corresponds to the polymer backbone degradation. The TGA thermograms indicated that the initial weight losses were steeper for polymers with higher sulfonation degrees. Furthermore, the weight loss temperature of sulfonated polyimides decreased and broadened with increasing sulfonation levels. However, the onset temperature of the first weight loss was independent of the degree of sulfonation. Weight loss data in TGA curves of the sulfonated polymers were used to calculate the degree of sulfonation. Experimental and theoretical values were in good agreement with each other. The sulfonated five-membered polyimide membranes were aged in an air-oven at increasing temperatures (30-220 °C) for 30 min and then titrated with TMAH using non-aqueous potentiometric titration. All the films that were aged up to 220 °C were still completely soluble in DMAc. Moreover, the sulfonic acid groups were unchanged. In addition, several new flexible sulfonated and unsulfonated diamines and bis(naphthalic anhydride) monomers containing phosphineoxide [-P(O)-] or sulfone [-S(O)₂ -] moieties in their structure have been synthesized and characterized with various analytical techniques. The structural design of naphthalic polyimides by incorporating bis(naphthalic anhydrides) was one approach to give a better solubility and processability of their related products. Development of an iterative approach for defining the optimum degree of sulfonation that will produce the highest ionic conductivity while still retaining other important properties such as flexibility, strength, hydrolytic stability has been a goal of this research and will be discussed in the thesis. / Ph. D.

Thesis (Ph.D)--Chemical Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Koros, William; Committee Member: Beckham, Haskell; Committee Member: Eckert, Charles; Committee Member: Henderson, Cliff; Committee Member: Meredith, Carson. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (M.S.)--Rochester Institute of Technology, 1991. / Typescript. Includes bibliographical references.

Thesis (M.S.)--Rochester Institute of Technology, 2008. / Typescript. Includes bibliographical references (leaves 56-58).

Thesis (M.S.)--Ohio University, August, 1995. / Title from PDF t.p.

Thesis (Ph.D.)--Chemical Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Henderson, Cliff; Committee Member: Beckham, Haskell; Committee Member: Hess, Dennis; Committee Member: Koros, William; Committee Member: Tolbert, Laren.