Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisors: Keith P. Johnston and William J. Koros. Vita. Includes bibliographical references.

Master of Science / Department of Chemical Engineering / John R. Schlup / The cross-linking reaction of the polyimide Matrimid 5218 with ethylenediamine (EDA) in methanol was investigated using Fourier transform infrared (FTIR) spectroscopy. Peaks associated with breaking imide bonds and the formation of amide bonds were identified. Using an internal standard peak of 1014 cm⁻¹ allowed for quantitative analysis to be applied. The peak areas, calculated by slice area, were used for absorbance ratio analysis to follow the cross-linking reaction as a function of time. Lastly, the absorbance values for the decreasing peak 1718 cm⁻¹ were used to calculate the order of reaction for the reaction rate of the mechanism.

Thermoplastic polyimides (TPIs) exhibit high glass transition temperatures (Tgs), which make them useful in high performance applications. Amorphous and semicrystalline TPIs show sub-Tg relaxations, which can aid in improving strength characteristics through energy absorption. The a relaxation of both types of TPIs indicates a cooperative nature. The semicrystalline TPI shows thermo-irreversible cold crystallization phenomenon. The polymer liquid crystal (PLC) used in the blends is thermotropic and with longitudinal molecular structure. The small heat capacity change (ACP) associated with the glass transition indicates the PLC to be rigid rod in nature. The PLC shows a small endotherm associated with the melting. The addition of PLC to the semicrystalline TPI does not significantly affect the Tg or the melting point (Tm). The cold crystallization temperature (Tc) increases with the addition of the PLC, indicating channeling phenomenon. The addition of PLC also causes a negative deviation of the ACP, which is another evidence for channeling. The TPI, PLC and their blends show high thermal stability. The semicrystalline TPI absorbs moisture; this effect decreases with the addition of the PLC. The absorbed moisture does not show any effect on the degradation. The addition of PLC beyond 30 wt.% does not result in an improvement of properties. The amorphous TPI + PLC blends also show the negative deviation of ACP from linearity with composition. The addition of PLC causes a decrease in the thermal conductivity in the transverse direction to the PLC orientation. The thermomechanical analysis indicates isotropic expansivity for the amorphous TPI and a small anisotropy for the semicrystalline TPI. The PLC shows large anisotropy in expansivity. Even 5 wt. % concentration of PLC in the blend induces considerable anisotropy in the expansivity. Thus, blends show controllable expansivity through PLC concentration. Amorphous TPI + PLC blends also show excellent film formability. The amorphous TPI blends show good potential for applications requiring high thermal stability, controlled expansivity and good film formability.

Aromatic polyimides are interesting materials since they possess outstanding key properties such as thermoxidative stability, high mechanical strength, high modulus, excellent electrical properties, and superior chemical resistance. However, their low solubility makes them difficult to characterize, process and obtain high molecular weight polymer. In this report, we synthesized a series of precursor polymers that contains Diels-Alder (DA) adducts of anthracene. Different dienophiles were tried. These precursor polymers are soluble in common organic solvents such as chloroform and can be easily processed to thin films. Heating the film above 215 degree induce retro-DA reaction, which generated the fully aromatic polyimides in situ. The solid-state retro-DA reactions were monitored by ATR-FTIR and UV-Vis spectra. The fully aromatic polyimides are highly stable and their thin films are insoluble in organic solvents. Profilometry and AFM studies showed that after the thermal treatment, the films are smooth and pin-hole free, while the volumes decreased with a percentage close to the weight loss caused by retro-DA reaction. These Polymers can have a wide range of potential applications from thermal patterning polymers to organic photovoltaics.

Phenylindane monomers 5(6)-amino-1-(4-aminophenyl)-1,3,3-trimethylindane (DAPI), 5,6-diamino-1-(4-aminophenyl)-1,3,3-trimethylindane (TAPI) and 6-hydroxy-1-(4-hydroxyphenyl)-1,3,3-trimethylindane (DHPI) were synthesized and characterized. DAPI, as well as other diamines, were then utilized in solution step polycondensation with a number of commercially available dianhydrides using either the two-step ester-acid solution imidization or the high temperature solution imidization routes. High molecular weight soluble fully cyclized polyimides were successfully synthesized using a 1:1 molar ratio of dianhydride to diamine. The polyimides were film forming and were characterized by size exclusion chromatography (SEC), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and selective gas permeation methods, as well as other techniques. The O2 permeation and O2/N2 selectivity values obtained for materials prepared in this thesis are discussed in relation to the concept of an "upper bound", as defined in the literature concerning gas separation membranes. The series of polyimides based on DAPI and several dianhydrides were found to have high glass transition temperatures (247°C-368°C) and very good short-term thermal stability as shown by TGA, despite the partially aliphatic character of DAPI. The 5,5'-[2,2,2-trifluoro-1-(trifluoromethyl)ethylidene]bis-1,3-isobenzenefurandione (6FDA)/DAPI system also exhibited low weight loss under nitrogen at 400°C, which was comparable to that of a wholly aromatic polyimide based on 1,2,4,5-benzenetetracarboxylic dianhydride (PMDA)/4,4'-oxydianiline (ODA) which is known to have high thermal stability. In addition, the 6FDA/DAPI polyimides had a refractive index value of 1.571 from which the dielectric constant was calculated, giving an attractively low estimated value of 2.47. The rigid, bulky and isomeric structure of DAPI in the repeat unit imparted film forming characteristics that allowed production of solvent cast membranes which displayed a range of O2 permeability and O2/N2 selectivity characteristics. High O2 permeabilities were observed for polyimides in which the DAPI structure predominated in relation to the overall polymer repeat unit, i.e. in combination with low molar mass dianhydrides. The more flexible dianhydrides afforded a greater degree of molecular freedom and were thought to result in a more tightly packed polymer conformation which decreased the rate of gas penetration through thin films. The DAPI/3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA) system showed the best combination of O2 permeability and O2/N2 selectivity values (2.8Ba and 7.3, respectively). Modest variations in the DAPI isomeric ratio did not significantly effect the gas permselectivity properties. High molecular weight polyimides based on DAPI and BTDA were synthesized by three different routes. The ester-acid and thermal imidization methods produced polyimides with the highest Tgs and best thermal stability in air, as compared to the chemical imidization procedure. For example, a Tg increase of 22°C and a 68°C increase in the 5% weight loss were found for the ester-acid imidized DAPI/BTDA polyimide over those found for the chemically imidized version. The higher Tg and 5% weight loss values were attributed to the elimination of residual uncyclized amide acid moieties. Polyimides derived from 6FDA were synthesized by the high temperature solution imidization method. Thin films, cast from NMP, were tough and creasable and afforded high Tg (>295°C) systems with good thermal stability. When combined with rigid diamines, 6FDA contributed to high O2 permeation and moderate O2/N2 selectivity. The high O2 permeability was ascribed to hindered interchain packing attributed to the bulky CF3 groups. The exceptionally high oxygen permeability and O2/N2 selectivity values of the 9,9-bis(4-aminophenyl) fluorene (FDA)/6FDA system, were near the desirable "upper bound" for gas separation membrane materials, while those of 3,7-diamino-2,8-dimethyl-dibenzothiophene-5,5-dioxide (DDBT)/6FDA were actually above the upper bound. High performance polymers based on 4,4'-bis [4-(3,4-dicarboxyphenoxy)]biphenyl dianhydride (BPEDA), 2,2'-bis [4-(3,4-dicarboxyphenoxy)phenyl] propane dianhydride (BPADA), 2,2-bis(3-amino-4-methylphenyl)hexafluoroisopropylidene dianhydride (Bis-AT-AF) and 3,7-diamino-2,8-dimethyl-dibenxothiophene-5,5-dioxide (DDBT) were also synthesized in this work. Additionally, they were characterized with regard to molecular weight, glass transition temperature, and thermal stability. Polyimide systems containing hydroxyl moieties in the repeat unit were also investigated. Incorporation of hydroxyl moieties in the repeat unit enhanced chain stiffness via intermolecular hydrogen bonding and showed Tg increases of ~30°C Hydroxyl moieties also decreased the thermal stability values typically observed for polyimides. High O2/N2 selectivity was achieved with all of the 4,4'-diaminobiphenyl-3,3'-diol (HAB) containing polymers. However, these materials also had low O2 permeabilities, which suggested a tightly packed structure, possibly facilitated by hydrogen bonding. In contrast to suggestions in the literature, the comparison between a polyimide having pendant hydroxyl groups and another having the same repeat unit without them did not reveal a significant change in permselectivity behavior. The synthesis, characterization and crosslinking behavior of functional polyimides containing phenol, amine and acetylene moieties are also described. A crosslinking reaction of oligomers containing phenol moieties with a tetrafunctional epoxy resin was achieved 100°C below the "dry" glass transition temperature and was attributed to residual solvent. Utilization of this crosslinking mechanism could allow membrane optimization by investigating the influence of a number of variables, such as the concentration of the phenolic moiety, epoxy weight percent, catalyst concentration and residual solvent content. / Ph. D.

Dans ce travail, on étudie la conception de membranes à base de polyimide et des membranes à matrices mixtes pour la séparation du mélange de gaz CO2/CH4. Une première série de membranes était entièrement constituée de polyimides. La synthèse et la fabrication des membranes a permis l'optimisation des propriétés de transport comme la perméabilité et la sélectivité pour les gaz purs et les mélanges gazeux. Par la suite, les propriétés de transport de gaz des membranes homo-polyimide (6FDA-ODA) et co-polyimides (6FDA-ODA/TeMPD) ont été étudiées pour différents rapports molaires de diamines (ODA et TeMPD). La perméabilité et le facteur de séparation en fonction de la fraction molaire de CO2 dans l'alimentation sont rapportés. Ensuite, les propriétés des membranes de polyimides (6FDA-ODA et 6FDA-ODA/TeMPD) réticulé par l'APTMDS sont rapportées en fonction du temps d'immersion ou de la concentration d'APTMDS. Dans ce cas, les résultats montrent que la performance des membranes 6FDA-ODA modifiées est au-dessus de la courbe limite supérieure de Robeson et que les membranes modifiées peuvent supporter des pressions assez élevées car la plastification est pratiquement éliminée. Finalement, des membranes composites sont produites en se servant de zeolites et de MOF comme phase dispersée dans le polyimide à base de 6FDA-ODA. La zéolite FAU/EMT greffée par l'aminopropyl méthyle éthoxysilane dans des solvants de polarités différentes et plusieurs types de MOF tels que MIL-53 et UIO-66 fonctionnalisés par des groupements amine sont étudiés. Les résultats montrent que les performances des MMM à base de 6FDA-ODA avec 25% poids de zéolite et différentes concentrations de A1-MIL-53-NH2 sont excellents pour la séparation CO2/CH4. Une étude détaillée de la relation entre les propriétés des membranes MMM et leur morphologie, selon leurs interactions avec l'aminé greffée sur la phase inorganique et l'agent de reticulation, est aussi rapportée.

The behavior of 8-harness satin woven Celion 3000/PMR-15 graphite-polyimide was experimentally investigated. Unnotched and center-notched specimens from (0)₁₅, (0)₂₂, and (0,45,0, - 45,0,0, - 45,0,45,0)₂ laminates were tested. Material properties were measured and damage development documented under monotonic tension, sustained incremental tension, and tension-tension fatigue loading. Damage evaluation techniques included stiffness monitoring, penetrant-enhanced X-ray radiography, laminate deply, and residual strength measurement. Material properties of the woven graphite-polyimide were comparable to those of woven graphite-epoxy. Damage development in woven graphite-polyimide was quite different than in non-woven graphite-epoxy. Matrix cracking was denser and delamination less extensive in the graphite-polyimide material system, and as a result, increases in notched residual tensile strength were much lower. A ply level failure theory was used to successfully predict the notched tensile strength of the (0,45,0, - 45,0,0, - 45,0,45,0)₂ laminate based on experimental data from the (0)₂₂ laminate. A simple method was used to simulate fatigue damage in a (0)₂₂ notched specimen to predict residual strength as a function of fatigue life. The advantages and disadvantages of the ply level failure theory used in this study are discussed. / Master of Science

The hybridization of direct write (DW) and additive manufacturing (AM) technologies to create additively manufactured electronics (AME) has enabled the integration of electrical functionality to form multifunctional AM components. Current work in AME has demonstrated the integration of conductive traces into and onto geometries and form factors that are not possible through traditional electronics packaging processes. This has largely been accomplished by using AM and DW technology to deposit conductive inks to form interconnects on the surface of AM substrates or within multimaterial AM geometries. However, the requisite thermal post-processing and high resistivity of the conductive inks and the limitations in thermal and dielectric performance of printable substrates commonly used in AME restrict the capabilities of these parts. This thesis proposes an alternative process for the conformal deposition of low resistivity traces on additively manufactured all-aromatic polyimides (AM-PI) without the use of conductive inks. This is accomplished through the selective patterning of laser induced graphene (LIG), a porous 3D graphene fabricated via laser irradiation, onto the AM-PI. While the resultant LIG is conductive, its resistivity is further reduced by the electrodeposition of copper (Cu-LIG). In this thesis, the synthesis of LIG on AM-PI, thermally post processed to 240℃, 300℃, and 450℃, is demonstrated and characterized through sheet resistance measurements and Raman spectroscopy. AM-PI post-processed to 300℃ demonstrated the lowest resistivity LIG formation (13.8 Ω/square). The resistivity of Cu-LIG is compared to an industry standard silver ink (Micromax CB028) used in direct write hybrid manufacturing applications. Cu-LIG was found to have a measured resistivity (1.39e-7 Ω·m), two orders of magnitude lower than the measured resistivity of the CB028 silver ink (1.62e-5 Ω·m). Additionally, the current capacity of the Cu-LIG was demonstrated and Joule heating of the material was observed via IR thermography. Cu-LIG demonstrated no failure of conductive trace or substrate under 5A of current for 2 minutes, heating to a maximum recorded temperature of 76.3℃. Several multifunctional components were fabricated as case studies to further validate the process. Several small passive electronic devices (e.g., a heater and an interdigitated capacitor) are fabricated to demonstrate selective deposition of complex copper traces. The fabrication of an Archimedes spiral on a hemispherical substrate via Cu-LIG is completed to demonstrate the ability to use the process to fabricate conformal conductive traces. An LED circuit is fabricated on a face-center cubic AM-PI lattice which demonstrates multi-planar fabrication on geometrically complex 3D printed substrates. / Master of Science / The hybridization of direct write (DW) and additive manufacturing (AM) technologies to create additively manufactured electronics (AME) has enabled the fabrication of AM components which have electronic functionality. Current work in AME has demonstrated the integration of conductive traces into and onto geometries and form factors that are not possible through traditional electronics packaging processes. This has largely been accomplished through the deposition of conductive inks to form interconnects on the surface of AM substrates or within multimaterial AM geometries. However, these conductive inks require thermal post-processing temperatures which exceed the thermal performance of common AM substrates. The dielectric performance of AM substrates is also restrictive to the capabilities of these parts. This thesis proposes an alternative process for the conformal deposition of low resistivity traces on high performance additively manufactured all-aromatic polyimides (AM-PI) without the use of conductive inks. This is accomplished through the selective patterning of laser induced graphene (LIG), a porous 3D graphene fabricated via laser irradiation, onto the AM-PI. While the resultant LIG is conductive, its resistivity is further reduced by the electrodeposition of copper (Cu-LIG). In this thesis, the synthesis of LIG on AM-PI, thermally post processed to 240℃, 300℃, and 450℃, is demonstrated and characterized through sheet resistance measurements and Raman spectroscopy. AM-PI post-processed to 300℃ demonstrated the lowest sheet resistance LIG formation (13.8 Ω/square). The resistivity of Cu-LIG is compared to an industry standard silver ink (Micromax CB028) used in direct write hybrid manufacturing applications. Cu-LIG was found to have a measured resistivity (1.39e-7 Ω·m), two orders of magnitude lower than the measured resistivity of the CB028 silver ink (1.62e-5 Ω·m). Additionally, the thermal performance and current capacity of the Cu-LIG was demonstrated by observing resistive heating of the material under current load via IR thermography. Cu-LIG demonstrated no failure of conductive trace or substrate under 5A of current for 2 minutes, heating to a maximum recorded temperature of 76.3℃. Several multifunctional components were fabricated as case studies to further validate the process. A heater and an interdigitated capacitor are fabricated to demonstrate selective deposition of complex copper traces. The fabrication of an Archimedes spiral on a dome via Cu-LIG is completed to demonstrate the ability to use the process to fabricate conformal conductive traces. An LED circuit is fabricated on an AM-PI lattice which demonstrates multi-planar fabrication on geometrically complex 3D printed substrates.

Trimesoyl chloride (TMC) crosslinked poly(vinyl alcohol) (PVA) / chitosan (CS) membranes and synthetic polyimide membranes were prepared for pervaporation dehydration of isopropanol and gas separation. PVA membranes were interfacially crosslinked with different amounts of TMC/hexane, and the degree of crosslinking was characterized by Fourier Transform Infrared Spectroscopy - Attenuated Total Reflectance Spectroscopy (FTIR-ATR) and water uptake. The asymmetric structure of the PVA-TMC membranes was revealed by FTIR-ATR. Thermal analysis was performed to understand the pyrolysis mechanism, which was supposed to be a combination of elimination of water and/or trimesic acid followed by breakage of the main chain. Water permeation and pervaporation dehydration of isopropanol were conducted, and the results showed that PVA-3TMC had the best overall pervaporation properties among the four PVA-TMC membranes studied. Sorption properties and pervaporation behavior of the PVA-3TMC membrane were investigated. The effects of water/isopropanol on the polymer matrix and the possible change of the degree of crystallinity induced by the sorbed water were believed to account for the sorption properties. For water permeation and pervaporation dehydration of isopropanol in a heating-cooling cycle, the permeation flux did not change significantly, and the selectivity was improved by the formation of crystallites during the heating run. For pervaporation in the diluting and concentrating runs at 60 °C, there was no change in the membrane permeability. Chitosan membranes were interfacially crosslinked in TMC/hexane with different crosslinking time. The membrane with a higher degree of crosslinking showed a higher degree of swelling in water at room temperature. A two-stage thermal decomposition mechanism was proposed based on thermal analyses. Pure gas permeation was performed with CO2 and N2 at room temperature, and CS-TMC-2 showed the best performance, with a CO2 permeability of ~163 Barrer and a CO2/N2 permeability ratio of ~42. Pervaporation was carried out for dehydration of isopropanol with the unconditioned and conditioned membranes, and the CS-TMC-3 membrane showed the best pervaporation performance. Pervaporation and gas separation properties were affected by the crosslinking-induced relaxation and the mobility/packing properties of the CS-TMC matrices. 4,4'-(Hexafluoroisopropylidene) diphthalic anhydride (6FDA)-based and 2,2-bis[4-(3,4-dicarboxyphenoxy) phenyl]propane dianhydride (BPADA)-based copolyimides were synthesized from one-step high-temperature polymerization in m-cresol. Polymers were characterized with Gel Permeation Chromatography (GPC), FTIR, Nuclear Magnetic Resonance Spectroscopy (NMR), Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). Surface free energies and interfacial free energies were calculated from contact angles to characterize hydrophilicity of the polyimide membranes. Gas permeation properties of 6FDA-based copolyimide membranes were studied with N2, O2, H2, He and CO2, and pervaporation dehydration of isopropanol was performed with 6FDA-based and BPADA-based membranes. An empirical linear moiety contribution approach was proposed, and the moiety contribution factors were used to illustrate the effects of dianhydrides and diamines on permselectivities of the copolyimide membranes. Bulky side groups, flexibility of polymer main chains, structures of monomer moieties, and interactions between gas molecules and polymer chains were shown to affect gas permselectivities, while in pervaporation, both sorption and diffusion properties were affected by the interactions between penetrants and polymer matrices as well as the steric effects of monomer moieties.

Trimesoyl chloride (TMC) crosslinked poly(vinyl alcohol) (PVA) / chitosan (CS) membranes and synthetic polyimide membranes were prepared for pervaporation dehydration of isopropanol and gas separation. PVA membranes were interfacially crosslinked with different amounts of TMC/hexane, and the degree of crosslinking was characterized by Fourier Transform Infrared Spectroscopy - Attenuated Total Reflectance Spectroscopy (FTIR-ATR) and water uptake. The asymmetric structure of the PVA-TMC membranes was revealed by FTIR-ATR. Thermal analysis was performed to understand the pyrolysis mechanism, which was supposed to be a combination of elimination of water and/or trimesic acid followed by breakage of the main chain. Water permeation and pervaporation dehydration of isopropanol were conducted, and the results showed that PVA-3TMC had the best overall pervaporation properties among the four PVA-TMC membranes studied. Sorption properties and pervaporation behavior of the PVA-3TMC membrane were investigated. The effects of water/isopropanol on the polymer matrix and the possible change of the degree of crystallinity induced by the sorbed water were believed to account for the sorption properties. For water permeation and pervaporation dehydration of isopropanol in a heating-cooling cycle, the permeation flux did not change significantly, and the selectivity was improved by the formation of crystallites during the heating run. For pervaporation in the diluting and concentrating runs at 60 °C, there was no change in the membrane permeability. Chitosan membranes were interfacially crosslinked in TMC/hexane with different crosslinking time. The membrane with a higher degree of crosslinking showed a higher degree of swelling in water at room temperature. A two-stage thermal decomposition mechanism was proposed based on thermal analyses. Pure gas permeation was performed with CO2 and N2 at room temperature, and CS-TMC-2 showed the best performance, with a CO2 permeability of ~163 Barrer and a CO2/N2 permeability ratio of ~42. Pervaporation was carried out for dehydration of isopropanol with the unconditioned and conditioned membranes, and the CS-TMC-3 membrane showed the best pervaporation performance. Pervaporation and gas separation properties were affected by the crosslinking-induced relaxation and the mobility/packing properties of the CS-TMC matrices. 4,4'-(Hexafluoroisopropylidene) diphthalic anhydride (6FDA)-based and 2,2-bis[4-(3,4-dicarboxyphenoxy) phenyl]propane dianhydride (BPADA)-based copolyimides were synthesized from one-step high-temperature polymerization in m-cresol. Polymers were characterized with Gel Permeation Chromatography (GPC), FTIR, Nuclear Magnetic Resonance Spectroscopy (NMR), Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). Surface free energies and interfacial free energies were calculated from contact angles to characterize hydrophilicity of the polyimide membranes. Gas permeation properties of 6FDA-based copolyimide membranes were studied with N2, O2, H2, He and CO2, and pervaporation dehydration of isopropanol was performed with 6FDA-based and BPADA-based membranes. An empirical linear moiety contribution approach was proposed, and the moiety contribution factors were used to illustrate the effects of dianhydrides and diamines on permselectivities of the copolyimide membranes. Bulky side groups, flexibility of polymer main chains, structures of monomer moieties, and interactions between gas molecules and polymer chains were shown to affect gas permselectivities, while in pervaporation, both sorption and diffusion properties were affected by the interactions between penetrants and polymer matrices as well as the steric effects of monomer moieties.