Neste trabalho, materiais nanocompósitos de poli(imida) (PI) derivada de BTDA-pFDA-Mel e argila do tipo montmorilonita, organicamente modificada (O-MMT), foram sintetizados usando a metodologia de two-steps. O componente inorgânico do nanocompósito foi adicionado nas concentrações de 3,3, 5,3 e 8,3% em massa. As membranas sintetizadas foram caracterizadas por Espectroscopia de Absorção na Região do Infravermelho com Transformada de Fourrier (FTIR), Difração de Raio X (DRX), Termogravimetria (TG), Espectroscopia de Fotoelétrons Excitados por Raio X (XPS) e Microscopias Ótica (MO), Eletrônica de Varredura (MEV) e de Transmissão (MET). Os resultados comprovam a formação de PI e uma estrutura de nanocompósito do tipo intercalado, onde a cadeia polimérica expulsa o surfactante do espaço interlamelar; além de apresentar estruturas de argila parcialmente esfoliadas. Os materiais sintetizados foram avaliados como polieletrólito em célula a combustível alcalina (Alkaline Fuel Cell - AFC), obtendo condutividades iônicas em torno de 0,032 S cm-1 e de 0,017 S cm-1 para as membranas de PI pura e de nanocompósito com 3,3% de argila em massa, respectivamente, ambas a 60 °C, as quais são na ordem ou até mesmo superior que os polieletrólitos comercias (Tokuyama®, 0,014 S cm-1) para eletrólito alcalino. Apesar de condutividades razoáveis, a performance obtida para as AFCs em operação não foram satisfatórias, desta forma, membranas de nanocompósitos com PI de cadeia principal de maior mobilidade foram sintetizadas, caracterizadas e avaliadas nas AFCs. Ademais, neste segundo nanocompósito, a adição de grupamentos amino na cadeia principal foram realizados para aumentar a condutividade iônica. Assim, este segundo material apresentou uma maior performance nas AFCs quando comparado com o nanocompósito de PI de cadeia mais rígida e com a membrana comercial Tokuyama® nas mesmas condições. Além disso, a carbonização superficial das amostras foi realizada por meio de tratamento térmico. A formação de estruturas grafitizadas nos materiais de PI pura e dos nanocompósitos foram investigadas por FTIR, DRX, TG, XPS e EPR. Foi encontrado que a formação de estruturas do tipo grafite nas amostras ocorrem principalmente nas primeiras camadas (grafitização superficial), preservando a estrutura interna da poli(imida). Com isso, estruturas poliméricas ou nanocompósitos com superfícies grafitizadas podem atuar tanto como polieletrólitos e ser um caminho promissor para o desenvolvimento de arranjos eletrodo-membrana (Membrane Electrode Assembly - MEA) mais eficientes para células a combustíveis alcalinas, como em processos de catálise heterogênea e processos de separação com membranas. / In this work, Poli(imide)/clay (PI/clay) nanocomposite membranes were synthesized by employing a two-steps method using organically modified montmorillonite clay (O-MMT) with different amounts of O-MMT loading (3.3, 5.3 and 8.3 wt.%). Fourier transform infrared spectroscopy (FTIR), X-ray power diffraction (XRD), thermogravimetric analysis (TG), X-ray photoelectron spectroscopy (XPS), optical microscopy (OM), scanning electron microscope (SEM) and transmission electron microscopy (TEM) measurements, confirmed the formation of pure PI and intercalated-nanocomposite structures. The results revealed parallel clay layers with interlamellar PI and some organoclay partially exfoliated. In addition, the polyelectrolyte membranes of PI and PI/O-MMT (3.3 wt.%) showed that the ionic conductivity were 2- and 1-fold, respectively, higher than that of commercial membrane (Tokuyama®, 0.014 S cm-1), in alkaline fuel cells (AFC) at 60 °C. Despite the fact that the membranes of pure PI and PI/O-MMT demonstrated a good degree of ionic conductivity, rapid fuel cell performance deactivation occurred for the temperature higher than 75 °C. Furthermore, the lack of prepared polyelectrolyte ionic groups, led us to consider alternative synthesis of PI/clay nanocomposite membranes. Thus, the performance for second polyelectrolyte was superior when compared to pure PI, PI/O-MMT and commercial Tokuyama® membranes at same conditions. Moreover, the samples were also surface carbonized by thermal treatment. Combining FTIR, XRD, TG, XPS and electron paramagnetic resonance (ESR) analysis, the results suggested that graphitized nanostructures formation occurred mainly on the surface, maintaining the PI bulk structure. Therefore, graphitized PI/clay membranes may act as one promising way for enhancing both membrane electrode assembly in alkaline fuel cells and gas separation or catalysis.

Neste trabalho, materiais nanocompósitos de poli(imida) (PI) derivada de BTDA-pFDA-Mel e argila do tipo montmorilonita, organicamente modificada (O-MMT), foram sintetizados usando a metodologia de two-steps. O componente inorgânico do nanocompósito foi adicionado nas concentrações de 3,3, 5,3 e 8,3% em massa. As membranas sintetizadas foram caracterizadas por Espectroscopia de Absorção na Região do Infravermelho com Transformada de Fourrier (FTIR), Difração de Raio X (DRX), Termogravimetria (TG), Espectroscopia de Fotoelétrons Excitados por Raio X (XPS) e Microscopias Ótica (MO), Eletrônica de Varredura (MEV) e de Transmissão (MET). Os resultados comprovam a formação de PI e uma estrutura de nanocompósito do tipo intercalado, onde a cadeia polimérica expulsa o surfactante do espaço interlamelar; além de apresentar estruturas de argila parcialmente esfoliadas. Os materiais sintetizados foram avaliados como polieletrólito em célula a combustível alcalina (Alkaline Fuel Cell - AFC), obtendo condutividades iônicas em torno de 0,032 S cm-1 e de 0,017 S cm-1 para as membranas de PI pura e de nanocompósito com 3,3% de argila em massa, respectivamente, ambas a 60 °C, as quais são na ordem ou até mesmo superior que os polieletrólitos comercias (Tokuyama®, 0,014 S cm-1) para eletrólito alcalino. Apesar de condutividades razoáveis, a performance obtida para as AFCs em operação não foram satisfatórias, desta forma, membranas de nanocompósitos com PI de cadeia principal de maior mobilidade foram sintetizadas, caracterizadas e avaliadas nas AFCs. Ademais, neste segundo nanocompósito, a adição de grupamentos amino na cadeia principal foram realizados para aumentar a condutividade iônica. Assim, este segundo material apresentou uma maior performance nas AFCs quando comparado com o nanocompósito de PI de cadeia mais rígida e com a membrana comercial Tokuyama® nas mesmas condições. Além disso, a carbonização superficial das amostras foi realizada por meio de tratamento térmico. A formação de estruturas grafitizadas nos materiais de PI pura e dos nanocompósitos foram investigadas por FTIR, DRX, TG, XPS e EPR. Foi encontrado que a formação de estruturas do tipo grafite nas amostras ocorrem principalmente nas primeiras camadas (grafitização superficial), preservando a estrutura interna da poli(imida). Com isso, estruturas poliméricas ou nanocompósitos com superfícies grafitizadas podem atuar tanto como polieletrólitos e ser um caminho promissor para o desenvolvimento de arranjos eletrodo-membrana (Membrane Electrode Assembly - MEA) mais eficientes para células a combustíveis alcalinas, como em processos de catálise heterogênea e processos de separação com membranas. / In this work, Poli(imide)/clay (PI/clay) nanocomposite membranes were synthesized by employing a two-steps method using organically modified montmorillonite clay (O-MMT) with different amounts of O-MMT loading (3.3, 5.3 and 8.3 wt.%). Fourier transform infrared spectroscopy (FTIR), X-ray power diffraction (XRD), thermogravimetric analysis (TG), X-ray photoelectron spectroscopy (XPS), optical microscopy (OM), scanning electron microscope (SEM) and transmission electron microscopy (TEM) measurements, confirmed the formation of pure PI and intercalated-nanocomposite structures. The results revealed parallel clay layers with interlamellar PI and some organoclay partially exfoliated. In addition, the polyelectrolyte membranes of PI and PI/O-MMT (3.3 wt.%) showed that the ionic conductivity were 2- and 1-fold, respectively, higher than that of commercial membrane (Tokuyama®, 0.014 S cm-1), in alkaline fuel cells (AFC) at 60 °C. Despite the fact that the membranes of pure PI and PI/O-MMT demonstrated a good degree of ionic conductivity, rapid fuel cell performance deactivation occurred for the temperature higher than 75 °C. Furthermore, the lack of prepared polyelectrolyte ionic groups, led us to consider alternative synthesis of PI/clay nanocomposite membranes. Thus, the performance for second polyelectrolyte was superior when compared to pure PI, PI/O-MMT and commercial Tokuyama® membranes at same conditions. Moreover, the samples were also surface carbonized by thermal treatment. Combining FTIR, XRD, TG, XPS and electron paramagnetic resonance (ESR) analysis, the results suggested that graphitized nanostructures formation occurred mainly on the surface, maintaining the PI bulk structure. Therefore, graphitized PI/clay membranes may act as one promising way for enhancing both membrane electrode assembly in alkaline fuel cells and gas separation or catalysis.

A series of mixed matrix membranes based on zeolites incorporated into fluorinated polyimides were fabricated and characterized in this study. The first system consisted of a polyimide (6FDA-6FpDA-DABA) with carboxylic acid groups incorporated into its backbone and amine-functionalized zeolite particles (ZSM-2). FTIR indicated that these functional groups interacted with each other through hydrogen bonding. Both SEM and TEM images revealed good contact between the polyimide and the zeolite. Permeability studies showed a drop in He permeability suggesting there were no voids between the two components. While simple gases such as O2 and N2 followed effective permeabilities predicted by mixing theories, polar gases such as CO₂ did not. The second system fabricated used the same polyimide with amine-functionalized zeolite L. This zeolite differs from ZSM-2 in that zeolite L's pores are not clogged with an organic template, and it possesses 1-D pores as opposed to ZSM-2's 3-D pore structure. XPS and zeta potential experiments were performed to verify the presence of amine groups on the zeolite surfaces. FTIR data showed that after a heat treatment, amide linkages were created between the amine group on the zeolite and the carboxylic acid group of the polyimide. SEM images showed a good distribution of zeolite L throughout the polymer matrix, and no indication of voids between the two components. Permeability experiments were performed to determine if the addition of zeolite L to the polyimide improved its separation performance. The permeability was unchanged between the pure polyimide membrane and the mixed matrix membrane, suggesting there were no voids present within the matrix. Permeability results of larger gases followed a Maxwell Model. A third system was prepared using a poly(imide siloxane) (6FDA-6FpDA-PDMS) and untreated zeolite L. The primary focus of this investigation was to determine if the addition of the flexible segment would promote direct contact with the zeolite surface and remove the need to amine-functionalize the zeolite. Poly(imide siloxane)s were synthesized at 0, 22, and 41 wt % PDMS as verified using 1H-NMR. FTIR was employed to qualitatively verify the successful imidization of the polymers. SAXS patterns and TEM images did not reveal distinct phases indicative of phase separation, however, AFM images did show the presence of phase separation of the surfaces of the poly(imide siloxane)s. Permeability results showed a decrease in selectivity and an increase in permeability as the wt % of PDMS was increased. Permeabilities and selectivities dropped as the zeolite loading was increased from 0 to 20 wt %. Upon increasing the zeolite loading from 20 to 30 wt %, increases in permeability were observed, but both the permeability and selectivity were still below that of the pure polymer. The final system studied employed the 41 wt % PDMS poly(imide siloxane) as the polymer matrix and either closed-ended or open-ended carbon nanotubes as the filler. SEM images showed regions of agglomeration for both types of nanotubes. Helium permeability dropped in both types MMMs, but more so in closed-ended carbon nanotubes MMM. Nitrogen permeability was unchanged for the closed-ended carbon nanotubes MMM, and dropped slightly in the open-ended carbon-nanotube MMM. / Ph. D.

Nesse trabalho obtiveram-se membranas de poli(imida) ramifricada com tamanho de poro ajustável usando melamina como agente de ramificação e indutor da formação de poros. Estas poli(imidas) foram sulfonadas usando-se ácido sulfúrico concentrado eficazmente. Finalmente, obtivemos membranas de carbono molecular por pirólise sob atmosfera inerte das poli(imidas) ramificadas. Estas membranas apresentam canais micrométricos paralelos à superfície e uma estrutura assimétrica constituída de uma camada densa filtrante e uma camada com canais micrométricos paralelos à superfície altamente ordenados. A membrana apresentou boa estabilidade química frente ao ataque por radicais hidroxila gerados via reação de Fenton. / In this work was obtained branched poly(imides) with tuned pore size using melamine as branching and pore induction agent. The poly(imides) with were efficiently sulfonated with concentrated sulfuric acid. Finally, the molecular sieve carbon membranes were obtained by pyrolysis under inert atmosphere of the branched poly(imides). These membranes have an asymmetric structure with a dense filtering layer and a porous layer with highly ordered channels standing parallel to the surface. These membranes display good chemical stability toward hydroxyl radical attack produced by Fenton reaction.

Nesse trabalho obtiveram-se membranas de poli(imida) ramifricada com tamanho de poro ajustável usando melamina como agente de ramificação e indutor da formação de poros. Estas poli(imidas) foram sulfonadas usando-se ácido sulfúrico concentrado eficazmente. Finalmente, obtivemos membranas de carbono molecular por pirólise sob atmosfera inerte das poli(imidas) ramificadas. Estas membranas apresentam canais micrométricos paralelos à superfície e uma estrutura assimétrica constituída de uma camada densa filtrante e uma camada com canais micrométricos paralelos à superfície altamente ordenados. A membrana apresentou boa estabilidade química frente ao ataque por radicais hidroxila gerados via reação de Fenton. / In this work was obtained branched poly(imides) with tuned pore size using melamine as branching and pore induction agent. The poly(imides) with were efficiently sulfonated with concentrated sulfuric acid. Finally, the molecular sieve carbon membranes were obtained by pyrolysis under inert atmosphere of the branched poly(imides). These membranes have an asymmetric structure with a dense filtering layer and a porous layer with highly ordered channels standing parallel to the surface. These membranes display good chemical stability toward hydroxyl radical attack produced by Fenton reaction.

The vast majority of commercial gas separation membrane systems are polymeric because of processing feasibility and cost. However, polymeric membranes designed for gas separations have been known to have a trade-off between permeability and selectivity as shown in Robeson's upper bound curves. The search for membrane materials that transcend Robeson's upper bound has been the critical issue in research focused on membranes for gas separation in the past decade. To that end, many researchers have explored the idea of mixed matrix membranes (MMMs). These membranes combine a polymer matrix with inorganic molecular sieves such as zeolites. The ideal filler material in MMMs should have excellent properties as a gas adsorbent or a molecular sieve, good dispersion properties in the polymer matrix of submicron thickness, and should form high quality interfaces with the polymer matrix. In order to increase gas permeance and selectivity of polymeric membranes by fabricating MMMs, we have fabricated mixed matrix membranes using carbon nanotubes (CNTs) and nano-sized mesoporous silica. Mixed matrix membranes containing randomly oriented CNTs showed that addition of nanotubes to a polymer matrix could improve its selectivity properties as well as permeability by increasing diffusivity. Overall increases in permeance and diffusivity for all tested gases suggested that carbon nanotubes can provide high diffusivity tunnels in the CNT within the polymer matrix. This result agreed well with molecular simulation estimations. In order to prepare ordered CNTs membranes, we have developed a simple, fast, commercially attractive, and scalable orientation method. The oriented CNT membrane sample showed higher permeability by one order of magnitude than the value predicted by a Knudsen model. This CNT membrane showed higher selectivities for CO₂ over other gas molecules because of preferential interaction of CO₂ with the amine functionalized nanotubes, demonstrating practical applications in gas separations. Recently, mesoporous molecular sieves have been used in MMMs to enhance permeability or selectivity. However, due to their micrometer scale in particle size, the composite membrane was extremely brittle and tended to crack at higher silica loading. In this study, we have developed fabrication techniques to prepare MMMs containing mesoporous MCM-41 nanoparticles on the order of ~50 nm in size. This smaller nanoparticle lead to higher polymer/particle interfacial area and provides opportunity to synthesize higher loading of molecular sieves in polymer matrix up to ~80 vol%. At 80 vol% of nano-sized MCM-41 silica loading, the permeability of the membrane increased dramatically by 300 %. Despite these increases in permeability, the separation factor of the MMMs changed only slightly. Therefore, these nanoscale molecular sieves are more suitable for commercialization of MMMs with very thin selective layers than are micro-sized zeolites or molecular sieves. / Ph. D.

Commercially available 4,4′-dichlorodiphenylsulfone (DCDPS) was successfully disulfonated with fuming sulfuric acid to yield 3,3′-disodiumsulfonyl-4,4′-dichlorodiphenylsulfone (SDCDPS). Subsequently, DCDPS and SDCDPS were systematically reacted with 4,4′-biphenol under nucleophilic step polymerization conditions to generate a series of high molecular weight, film-forming, ductile, ion conducting copolymers. These were converted to the acid form and investigated as proton exchange membranes for fuel cells. Hydrophilicity increased with the level of sulfonation. However, water sorption increased gradually until about 50 mole percent SDCDPS was incorporated, and thereafter showed a large increase to yield water soluble materials for the 100% SDCDPS system. Atomic force microscopy (AFM) confirmed that the morphology of the copolymers displayed continuity of the hydrophilic phase at 60 mole percent SDCDPS. Conductivity measurements in the 40-50 mole percent SDCDPS range, where excellent mechanical strength was maintained, produced values of 0.1 S/cm or higher which were comparable to the control, Nafion™. These compositions also show a high degree of compatibility with heteropolyacids such as phosphotungstic acid. These inorganic compounds provide a promising mechanism for obtaining conductivity at temperatures well above the boiling point of water and membrane compositions containing them are being actively pursued. The water soluble 100% SDCDPS system was further investigated by successfully functionalizing the endgroups to afford aromatic amines via appropriate endcapping with m-aminophenol. Oligomers and polymers from 5-30 kg/mole number average molecular weight were synthesized and well characterized by NMR spectroscopy, endgroup titrations and size exclusion chromatography. The diamino-telechelic sulfonated segment was reacted with several dianhydrides and diamines to produce multiblock, hydrophobic polyimide-hydrophilic sulfonated polyarylene ether copolymers. Both ester-acid and amic acid synthesis routes were utilized in combination with spin-casting and bulk imidization. A series of tough, film-forming segmented copolymers was prepared and characterized. AFM measurements demonstrated the generation of quite well defined, nanophase-separated morphologies which were dependent upon composition as well as aging in a humid environment. Characterizations of the segmented copolymers for conductivity, and water and methanol sorption were performed and comparisons to state-of-the-art perfluorinated Nafion™ systems were made. It is concluded that the segmented or block systems have the potential to enhance certain desirable PEM characteristics in fuel cells, particularly those related to swelling, retention of mechanical strength at elevated temperatures, and critical adhesion issues in membrane electrode assemblies. / Ph. D.