Virginia Polytechnic Institute and State University laboratories have produced a wide variety of polyimide films which have been modified by the incorporation of metal compounds. These polymer/metal composites have potential use as coatings in aerospace applications where enhanced electrical conductivity and thermal stability are desirable. Generally, these materials are produced by heating a polyamic acid solution which contains a soluble metal salt. While the electrical and thermal properties of some of these films have been studied in great detail, little is known about the factors which control the ultimate distribution of metal in the polymer matrix. In this work, the segregation of components in polyimide modified with the gold salt, HAuCl₄·H₂O, is described. Thermal treatment usually promoted three changes in the film: (1) conversion of an initially present polyamic acid to the thermally stable polyimide, (2) reduction of chloroauric acid to metallic gold and (3) redistribution of the metal into gold domains either in the bulk or at a surface of the film. The third event listed above has been termed metalization. Most of the gold modified polyimide I films exhibited bulk metalization as evidenced by the dispersion of very small gold particles through out the film. However, the gold aggregates which comprised the metalized surface layer possessed several different morphologies which indicated that a diffusion limited aggregation processes controlled the aggregate growth. The appearance of these aggregates was central to developing a model of phase separation in these metal modified films. / Ph. D.

Novel, polyand weight, randomly coupled, poly(imide siloxane) segmented copolymers were prepared and characterized. The copolymers were synthesized in two steps, the first involving the generation of soluble poly(amic acid) intermediates through reaction of various aromatic dianhydrides and aromatic diamines with a series of bis(aminopropyl)polydimethylsiloxane oligomers. These difunctional siloxane oligomers were prepared through the anionic equilibration of octamethylcyclotetrasiloxane with bis(3-aminopropyl)tetramethyldisiloxane in the presence of a siloxanolate catalyst. The aromatic monomers and siloxane oligomers were quantitatively reacted in a cosolvent system. The poly(amic acid) intermediates were then cyclodehydrated employing two different thermal treatments to afford the imidized homo- and copolymers. The first imidization process, conducted on solution cast poly(amic acid) films, employed stepwise heating cycles to 300°C. Quantitative thermal imidization was also achieved in solution at temperatures in the 140 to 170°C range. This novel method of imidization used a coamide solvent system. Kinetic studies employing FTIR indicated that the imidization process could be described by first order kinetics. An activation energy of 26 kcal/mole (109 kj/mole) was derived. The homopolymers and siloxane modified copolymers were characterized as a function of chemical composition and imidization method. Polymer solubility and processability greatly improved upon siloxane oligomer incorporation and the use of the solution imidization procedure. Regardless of the method of imidization, all homo- and copolymers possessed excellent thermal, mechanical, and adhesive properties. These properties were found to be a function of siloxane content and siloxane oligomer molecular weight. In all segmented copolymer systems, a two-phase microstructure developed at relatively low block molecular weights. X-ray photoelectron spectroscopy (XPS) results indicated that the surface of copolymer films was largely dominated by siloxane. Because of this, the siloxane modified copolymers advantageously displayed lower water uptake and much improved resistance to oxygen plasma degradation. XPS and SEM studies showed that the stabilization mechanism involved a siloxane to silicate transformation under an oxygen plasma environment. / Ph. D.

High molecular weight, soluble polyimides were synthesized by a non-traditional synthetic route utilizing solution imidization techniques and diester-diacid derivatives of various commercially available dianhydrides. "One pot" syntheses were conducted using a solvent system of N-methylpyrrolidinone and σ-dichlorobenzene at temperatures of 170°C to 180°C and times of 24 hours or less. The resulting polyimides were soluble in amide solvents at concentrations of 15 to 20 percent (w/v) at 25°C, were fully cyclodehydrated as determined by non-aqueous potentiometric titrations, possessed molecular weight distributions very close to the theoretical value of 2.0 and displayed glass transition temperatures consistent with accepted values for the same materials synthesized via conventional methods. Model studies indicated that polymerization proceeds via intermediate conversion of the esteracid functional groups to anhydride groups. This method was also successfully employed in the synthesis of controlled molecular weight ethynyl-functionalized thermosetting imides. High T_g's, low end group concentrations and the relatively low cure temperature of the ethynyl end group restricted sample fabrication to thin, solution-cast films; nevertheless, several of these systems were evaluated for high temperature stability and were identified as potential candidates for 700°F (371°C) applications. In addition, a novel polyimide synthesis utilizing diamine dihydrochlorides as substitutes for unstable diamines was also investigated, and a series of novel polyimides based on diaminoresorcinol and commercial dianhydrides was synthesized. Diaminoresorcinol dihydrochloride and dianhydride were heated in an NMP/dichlorobenzene mixture; at sufficiently high temperatures the insoluble dihydrochloride dissociates, liberating hydrogen chloride gas and the soluble free diamine, which rapidly dissolves and reacts with dianhydride before decomposition occurs. The poly(hydroxy-imide)s possess T_g's in excess of 250°C, are soluble in amide solvents and, as might be expected, are extremely hygroscopic. / Ph. D.

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.