Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Includes bibliographical references (leaves 255-263). Available also in a digital version from Dissertation Abstracts.

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It was the objective of this research to develop high temperature and high performance polyimides that also display (a) thermal stability; (b) crystallinity in the initial material and ability to crystallize from the melt; (c) fast crystallization kinetics and (d) melt processability. This unique combination of properties is presently unavailable in any other polyimide. In this regard, the present work investigates the crystallization, morphology and thermal stability of two novel semicrystalline polyimides based on the same diamine, 1,3-bis (4-aminophenoxy) benzene (TPER), but two different dianhydrides, 3,3',4',4'-biphenyltetracarboxylic dianhydride (BPDA) and 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA). Phthalic anhydride was used as an endcapper to improve the thermal stability of the polyimides. The BPDA based polyimide was also tested extensively as a structural adhesive using Ti-6Al-4V coupons. Additionally, these polyimides are based on monomers, that are presently commercially available. The bulk thermal stability of the polyimides was first evaluated using dynamic and isothermal thermogravimetric experiments. DSC was utilized to test the ability of the polyimides to crystallize from the melt after exposures to varying melt times and temperatures. Exceptional thermal stability was demonstrated by BPDA based polyimide with no change in the melting behavior after 40 min at 430°C or 30 min at 440°C. The semicrystalline morphology of the material was studied using hot stage polarized optical microscopy (OM) and atomic force microscopy. The spherulitic growth rates were determined as a function of crystallization temperature after quenching from various melt times and temperatures. The effect of crystallization temperature, previous melt time and melt temperature on the morphology was considered. The spherulitic growth rates increased with increasing undercooling in the temperature range studied (nucleation controlled), while the growth rate at a specific crystallization temperature decreased on increasing the previous melt time and temperature. The melting behavior was studied after different crystallization times and temperatures and also as a function of different heating rates. Crystallization kinetics was followed both isothermally and non-isothermally using DSC and OM. Avrami analysis was performed for TPER-BPDA and the obtained results were correlated with microscopic observations. Melt viscosity measurements were carried out as a function of melt temperature, melt time and frequency. The adhesive investigations for TPER-BTDA utilized lap-shear test, wedge test and double cantilever beam tests. The durability of the adhesive and the fracture surface was studied after exposure to various solvents and after high aging and testing temperatures. The polyimide demonstrated very high average room temperature lap-shear strengths (8400 psi or 59 MPa), excellent solvent resistance and durability of strengths at high aging and testing temperatures. / Ph. D.

Additive manufacturing provides unmatched control and diversity over structural design of polymeric, ceramic and metallic parts. Nevertheless, until recently, the toolbox of polymeric feedstocks for light based additive manufacturing limited employment of printed parts for applications necessitating high thermomechanical performance. Development of synthetic pathways permitted the first additive manufacturing of high performance poly(amide imides) via ultraviolet assisted direct ink write (UV-DIW) printing. Precursor resins exhibited prerequisite rheology and reactivity for UV-DIW and produced organogels were well-defined and self-supporting. Thermal treatment induced drying and imidization of the precursor organogels to form the desired poly(amide imide) structures. During post-processing the parts displayed linear isotropic shrinkage as low as 26% and exhibited competitive thermomechanical properties. Following expansion of the high performance backbones available for additive manufacturing, simplification of synthetic rigors was undertaken. This investigation facilitated the evolution of the first photocurable and processable small molecule polyimide precursors. These supramolecular carboxylate ammonium nylon salts, coined polysalts, allowed for additive manufacturing of both high performance polyimides and polyetherimides using vat photopolymerization (VP). The use of small molecule precursors over previously investigated polymeric precursors displayed much lower solution viscosities yielding reduction of organic solvent loading, inducing lower overall shrinkage. Polysalts provide a stimulating platform for rapid and facile printing of high performance polyimides in the future. Surveying the excellent carbonization behavior for aromatic polyimides spurred translation of known 2D protocols to post-processing of printed polyimides. Applying pyrolysis methodologies to parts produced using VP and UV-DIW induced efficient carbonization at 1000 °C. Remarkably, the carbonized parts retained structure and did not display cracks or pore formation. Raman spectroscopy indicated production of disordered carbon via the utilized pyrolysis protocol, in line with literature on carbonization of PMDA-ODA polyimide at 1000 °C. Electrical testing indicated production of conductive materials following pyrolysis, with carbonization temperature modulating the performance. The excellent thermal stability, transport properties, and known mechanical performance of carbonaceous materials may enable application of these printed objects in customized electronics and aerospace environments. Exploration of drop-in monomeric units permitted a multi-pronged research program into augmentation of mechanical, rheological and transport properties of high performance polyetherimides (PEIs). Installation of sodium or lithium substituted disulfonated monomers via classical two-step polyimide synthesis afforded two series of sulfonated polyetherimides (sPEI). The sPEIs exhibited robust thermal properties, with high sulfonate mol% inducing Tg > 300 °C. X-ray scattering experiments revealed the development of domains via inclusion of the sulfonate moieties, with low mol% producing larger domain spacing. The larger domains present in the low mol% sPEIs yielded improved ionic liquid uptake within 2 d, yielding improved ionic conductivities at room temperature relative to high mol% samples. The observed conductivities indicated potential of the sPEIs as battery electrolytes, but further ionic liquid incorporation is required for competitive performance. Development of a poly(ethylene glycol) (PEG) bearing macromonomer facilitated synthesis of PEIs and PI graft copolymers. When coupled with 4,4'-(4,4'-isopropylidene-diphenoxy)diphthalic anhydride (BPADA) and meta-phenylene diamine (mPD), the PEG-grafted materials exhibited signs of phase mixing at low mol% incorporation of macromonomer, with a single observable Tg depressed from neat BPADA-mPD. Doping of the PEI-g-PEG with lithium salts allowed for production of polymeric films that displayed good ionic conductivities at room temperatures. Extension of the PEG macromonomer into fully aromatic PIs yielded phase separated materials even at modest loadings, >2.5 mol%. The formed PEG-g-PMDA-ODA contained thermally stable PI main-chains with thermally labile graft chains, which when thermally treated induced facile quantitative PEG removal. Remarkably, the thermally treated materials retained flexibility, even at >60 wt.% PEG removal. Further investigations aim to explore use of novel PEIs in energy storage as well as low density and dielectric materials. / Doctor of Philosophy / High performance polymers enjoy wide use in microelectronics and aerospace industries due to high thermal stability and excellent mechanical performance. However, processing restrictions hinder manufacturing of 3-dimensional objects of many high performance polymers suitable for extreme environments. Additive manufacturing, also known as 3D printing, has garnered attention in both academic and industrial settings over the last four decades due to the unmatched control over part design and internal structure, but the material arsenal for additive manufacturing of polymers lacks options for applications demanding high thermal stability. The first half of this dissertation aimed to promote translation of high performance polymeric chemistries to suitable feedstocks for additive manufacturing. By designing and developing novel chemical pathways, traditional processing limitations were circumvented and high performance polymers, such as poly(amide imides) and polyimides, were successfully processed via light based additive manufacturing. Likewise, by investigating carbonization dynamics of polyimides and expanding current additive manufacturing techniques for processing of fully aromatic polyimides, complex 3D carbonaceous materials were obtained. These carbon objects present extreme thermal stability and electrical conductivity, advantageous for aerospace and electronic industries. Additionally, investigations allowed for development of synthetically facile routes for expanding the available polyimide backbones for additive manufacturing via use of small molecule precursors. The second half of the dissertation explored novel polyetherimide and polyimide reagents for production of functional materials. Harnessing ionic building blocks permitted synthesis of a series of thermally robust polyetherimides displaying promise for energy storage. Similarly, coupling previous literature for ion conduction in solid polymer electrolytes for battery applications with thermally stable and flame resistant polyetherimides enabled synthesis of a series of innovative graft copolymers with good room temperature ionic conductivities. Lastly, pairing of thermally labile polymers with thermally resistant polyimide backbones allowed for development of an exciting platform for obtaining highly insulting and flexible films for electronics applications. Outlined future work aims to probe the formation of pores in the obtained polymer

Fretting of solvent cast polyimide coatings was investigated in a ball-on-flat geometry as a function of relative humidity. Polyimides were synthesized from benzophenone tetracarboxylic dianhydride (BTDA) and bisanline (Bis P), 6-fluoro bis dian hydride (6FDA) and Bis P, and pyromellitic dianhydride (PMDA) and bis A phenyl phosphine oxide (BAPPO). Coating life - the time for the steel ball to wear through the coating - shortened with increasing humidity. Iron oxides or other reaction products from 52100 ball generated at high humidity acted as abrasives and accelerated the wear of the coatings. Variation of coating life among the three polyimides was attributed to the residual stress, which developed upon cooling from the annealing temperature due to the mismatch of thermal expansion coefficients between the polymer and the metal substrate. Calculated from elasticity theory, the normal stress dropped shortly after the start of the test, remained relatively constant, and increased toward the end. This variation correlated with the wear rate and accounted for the non-linear increase of coating life with coating thickness. Sub-surface shear stress and surface tensile stress predicted well, respectively, the debonded shape and the inter-crack spacing of Hertzian cracks. / Ph. D.

Fully imidized, high molecular weight polyimide homopolymers and random segmented poly(siloxane imide) and poly(aryl ether imide) copolymers were prepared for use as environmentally stable, tough structural matrix resins, structural adhesives, and dielectric materials. Although polyimides are well suited for such high performance engineering applications due to their excellent thermal and mechanical properties, their typical intractability in the fully imidized state has been a serious limitation. Therefore, this research has specifically focused upon several methods by which the processability of polyimide systems may be improved. One method involved the utilization of a solution imidization technique in converting the poly(amic acid) intermediate to the fully cyclized polyimide. Another important method was the incorporation of a monofunctional reagents to obtain controlled endgroups and molecular weights. Structural modifications achieved by either copolymerization with polydimethylsiloxane or polyaryl ether sulfones or ketones, or variation of the dianhydrides or diamines resulted in major strides in obtaining enhanced process ability, particularly when coupled with controlled molecular weight and the solution imidization technique. Significant reductions in the dielectric constant and water sorption, and improvements in processability were obtained by incorporating relatively nonpolar reactants, such as fluorinated dianhydrides, hydrophobic aromatic diamines, and polydimethylsiloxane oligomers. / Ph. D.

Polyimides, due to their high thermal stability, excellent chemical stability, useful mechanical properties, and extremely high electrical resistivity, are utilized in aerospace, electronic, and specialty consumer markets. However, in some applications, lower electrical resistivity is preferable. Toward this goal, polyimide films have been modified with metal salts and metal complexes. Depending upon processing conditions, the films contain ionic species uniformly distributed throughout their bulk, or are highly anisotropic structures containing near-surface metal or metal oxide. Evaluation of solvent cast films by a variety of analytical techniques has been used to develop structure-property-process correlations in cobalt chloride modified polyimides. To date, no interaction between the additive and the matrix has been indicated by ultraviolet, visible, or infrared spectroscopy, though by differential scanning calorimetry and a specialized thermogravimetry technique, some interaction is implied. Elemental analysis has verified that polyimides having a metal oxide surface also have residual bulk metal ion content. A major controller of the bulk resistivity of metal ion modified polyimide films was found to be the polymer glass transition temperature; a lower glass transition temperature resulted in lower electrical resistivity at a particular temperature. Central to this research work was the design and construction of a sensitive and reliable electrical resistivity measurement system. The system was also found useful for probing polymer contamination and molecular motion. Further, the electrical measurements indicated that uniformity between samples was poor. Modification of an inert gas oven, allowing processing in controlled atmosphere, proved that film surface conductivity is critically influenced by humidity. A model has been proposed that supports both the d.c. electrical properties and surface spectroscopic data. The model and details in the ceramic literature were the primary factors in pursuing a specific codoped polyimide system. With the codoped system, the electrical resistivity and activation energy for conduction, compared with either of the singly doped polyimide films, were predictably and favorably reduced. / Ph. D.

Polyimides are attractive polymers because of valued intrinsic properties such as high thermal stability and good solvent resistance. At the same time, much effort is put into modifying polyimides to introduce different properties. This thesis describes a study where polyimides were modified with soluble metal compounds in an effort to create microcomposite films in which the location of the composite structure was controlled; namely at the film interfaces. Two different modification techniques were used in this study, in-situ chemical generation and infusion deposition. Results indicate that infusion deposition was successful in producing a gradient microcomposite structure in polyimide films when silver(I)nitrate was the metal dopant. Analysis revealed that formation of the microcomposite structure depends upon the glass transition temperature and precure temperature of the polyimide film being modified. / Master of Science

Polyimides are well known for their high thermal stability, chemical inertness, and their high electrical resistance. These properties make them ideal for use in the aerospace and electronics industries. Often polyimides are modified by coating or doping the films with metal species to change the surface or bulk properties of the polyimide. Usually this is done to create an electrically conductive surface layer. Previously, surface layers of metal and/or metal oxide on polyimide films have been made by homogeneously doping a poly(amide acid) solution with a metal complex and then thermally curing to 300°C. However, much of the dopant remains in the bulk of the films. Depending on the nature of the metal salt or complex, it has been postulated that lower polymer decomposition temperatures result if residual dopant remains in the bulk of the polymer. Deposition by infusion of the metal salt or complex was proposed as an alternative method for developing surface layers on polyimide films. The infusion processes attempted and the resulting films will be described and discussed. / Master of Science

Poly(arylene ether sulfone) oligomers have been synthesized by nucleophilic aromatic substitution using potassium carbonate as base and N-methyl pyrrolidinone (NMP) as solvent. m-Aminophenol was used as an endcapper to control the molecular weight of the oligomers and to provide functional amine termination. These amine terminated oligomers can then be utilized in a variety of post reactions. Poly(arylene ether sulfone)-Polyimide segmented copolymers were synthesized using a solution imidization procedure with NMP as the solvent and o-dichlorobenzene as the azeotroping agent. The polysulfone oligomers were reacted into the system via the diamine oligomer. The segmented copolymers demonstrated good solubility characteristics, high thermal stability, and high glass transition temperatures. Previously, polyimides containing pyromellitic dianhydride (PMDA) did not remain soluble in the NMP solvent during the solution imidization, but rather precipitated out of solution when partially imidized. Incorporation of the amine terminated polysulfone oligomers into PMDA containing copolymers resulted in Systems that remained soluble even after completion of imidization. The resulting copolymers were completely soluble in many of the high boiling solvents. The copolymers demonstrated high thermal Stability and high glass transition temperatures. / Master of Science