For the last two decades, the possibility of using synthetic membranes for industrial gas separations has attracted considerable interest since membrane separation technologies have the advantages of energy efficiency, simplicity and low cost. However, for wider commercial utilization there is still a need to develop membranes with higher permeant fluxes and higher transport selectivities. Conductive polymers, due to their high gas transport selectivities, give rise to a new class of polymeric materials for membrane based gas separation though poor mechanical properties obstruct the applications for this purpose of use. This problem led researches to a new idea of combining the conducting polymers with insulating polymers forming mixed matrix composite membranes. In the previous studies in our group, polypyrrole was chosen as the conductive polymer, and different preparation techniques were tried and optimized for membrane application. As the insulating polymer, previously poly(bisphenol-Acarbonate) was used to support the conductive polymer filler in order to constitute a conductive composite membrane. For this study, as the polymer matrix, hexafluorobisphenol A based poly(arylene ether ketone) was targeted due to its physical properties and temperature resistance which can be important for industrial applications. First of all, permeabilities of N2, CH4, Ar, H2, CO2, and H2 were measured at varying temperatures ranging from 25&deg / C to 85&deg / C through a homogenous dense membrane of chosen polymeric material to characterize its intrinsic properties. Measurements were done using laboratory scale gas separation apparatus which makes use of a constant volume variable pressure technique. The permeability results were used for the calculations of permeation activation energies for each gas. These permeation activation energies were found to be differing slightly for each gas independently from the kinetic diameters of gases. In this study, mixed matrix membranes of conducting polymer, polypyrrole (PPy) and insulating polymer, hexafluorobisphenol A based poly(arylene ether ketone) (PAEK) were also prepared. It was observed that PAEK and PPy form a composite mixed matrix structure, which can function as permselective membrane. The effect of conducting polymer filler content was investigated with two different filler ratios. When comparing with the pure PAEK membranes, meaningful increases for both permeability and selectivity were obtained for some of the gases.

The purity of the disulfonated monomer, such as 3,3"-disulfonated-4,4"-dichlorodiphenyl sulfone (SDCDPS), was very important for obtaining high molecular weight copolymers and accurate control of the oligomer's molecular weight. A novel method to characterize the purity of disulfonated monomer, SDCDPS, was developed by using UV-visible spectroscopy. This allowed for utiliziation of the crude SDCDPS directly in the copolymerization to save money, energy, and time. Three series of tert-butylphenyl terminated disulfonated poly(arylene ether sulfone) copolymers (BPSH35, 6FSH35, and 6FSH48) with controlled molecular weightsï¼ Mnï¼ , 20 to 50 kg·mol-1, were successfully prepared by the direct copolymerization method. The molecular weight of the copolymer was controlled by a monofunctional monomer tert-butylphenyl, and characterized by the combination of 1H NMR spectra and modified intrinsic viscosity measurements in NMP with 0.05 M LiBr, which was added to suppress the polyelectrolyte effect. The mechanical properties of the membranes, such as the modulus, strength and elongation at break, were improved by increasing the molecular weights, but water uptake and proton conductivities found insensitive to copolymers" molecular weights. Three series of disulfonated poly(arylene ether ketone) random copolymers have been synthesized and comparatively studied, according to their different chemical structures, for use as proton exchange membranes. The copolymers containing more flexible molecular structures had higher water uptake and proton conductivity than the rigid structures at the same ion exchange capacity. This may be due to the more flexible chemical structures being able to form better phase separated morphology and higher hydration levels. A new hydrophobic-hydrophilic multiblock copolymer has been successfully synthesized based on the careful coupling of a fluorine terminated poly(arylene ether ketone) (6FK) hydrophobic oligomer and a phenoxide terminated disulfonated poly(arylene ether sulfone) (BPSH) hydrophilic oligomer. AFM images and the water diffusion coefficient results confirmed that the multiblock copolymer formed better proton transport channels. This multiblock copolymer showed comparable proton conductivity and fuel cell performance to the Nafion® control and had much better proton transport properties than random ketone copolymers under partially hydrated conditions. This suggested that the multiblock copolymers are promising candidates for proton exchange membranes especially for applications at high temperatures and low relative humidity. / Ph. D.

Poly(arylene ether sulfone)s with dendritic terminal groups were synthesized by step-growth polymerization of two difunctional monomers in the presence of preformed dendritic end-cappers. These polymers were characterized by NMR, SEC, DSC, TGA, melt rheology and tensile tests. The melt viscosities of these polymers in the high frequency region were lower than the control while the stress-strain properties were comparable to those of the control, suggesting that it is possible to reduce the high shear melt viscosities of this type of polymers without affecting the stress-strain properties by introducing bulky dendritic terminal groups. Poly(arylene ether sulfone)s with hyperbranched terminal groups were also synthesized. These polymers were synthesized by reacting fluoro-terminated poly(arylene ether sulfone) chains with an arylene ether ketone AB2 monomer. The terminal groups of these polymers were capped by tert-butylphenol. The results from NMR and SEC showed that multiple tert-butyl units were successfully introduced onto the polymer chains, suggesting that this synthetic method could be useful for introducing multiple functional groups onto the polymer chain ends in fewer synthetic steps than an analogous method using preformed dendritic end-cappers. It was also demonstrated that multiple sulfonated phenols were attached to the terminal groups of polysulfones by this method. A novel cyclohexyl-containing difunctional monomer was prepared and successfully incorporated into poly(arylene ether sulfone) backbones. These polymers were characterized by NMR, SEC, DSC, TGA, DMA and tensile tests and compared to terephthaloyl analogs. Tensile tests and DMA showed the cyclohexyl units impart a higher magnitude of secondary relaxation than the terephthaloyl units while maintaining high modulus, suggesting that these polymers may have higher impact strength than the ones with no cyclohexyl units. / Ph. D.

The following studies describe the synthesis and properties of a family of poly(arylene ether ketone)s which are well known to have good thermal stability, mechanical durability, and other film properties. These poly(arylene ether ketone)s were functionalized with fluorine, oxidized, blended, and crosslinked to increase performance with focus on materials for polymeric capacitors and gas separation membranes. There is a need for polymeric capacitors with improved energy storage density and thermal stability. In this work, the affect of polymer molecular structure and symmetry on Tg, breakdown strength, and relative permittivity was investigated. A systematic series of four amorphous poly(arylene ether ketone)s was compared. Two of the polymers had symmetric bisphenols while the remaining two had asymmetric bisphenols. Two contained trifluoromethyl groups while the other two had methyl groups. The symmetric polymers had Tg's of approximately 160 °C while the asymmetric polymers showed higher Tg's near 180 °C. The symmetric polymers had breakdown strengths near 380 kV/mm at 150 °C. The asymmetric counterparts had breakdown strengths near 520 kV/mm even at 175 °C, with the fluorinated polymers performing slightly better in both cases. The non-fluorinated polymers had higher relative permittivities than the fluorinated materials, with the asymmetric polymers being better in both cases. Two amorphous, high glass transition, crosslinkable poly(arylene ether)s for gas purification membranes have been studied. The polymers were polymerized via step growth and contained tetramethyl bisphenol F and either 4,4'-difluorobenzophenone or 4,4'-dichlorodiphenylsulfone. The benzylic methylene group in tetramethyl bisphenol F can undergo oxidation reactions and crosslinking with UV light. The polymers were oxidized under two different conditions, one by chemical treatment using oxone and KBr and one by elevated thermal treatment in air. Thermogravimetric analysis, 1H-NMR and attenuated total reflectance Fourier transform infrared spectroscopy revealed the progress of the thermal oxidation reactions. Both polymers produced tough, ductile films and gas transport properties of the non-crosslinked linear polymers and crosslinked polymer was compared. Crosslinking was performed by irradiating polymer films for one hour on each side in air under a 100W high intensity, long-wave UV lamp equipped with a 365-nm light filter. The O2 permeability of tetramethyl bisphenol F containing non-crosslinked poly(arylene ether ketone) was 2.8 Barrer, with an O2/N2 selectivity of 5.4. Following UV crosslinking, the O2 permeability decreased to 1.8 Barrer, and the O2/N2 selectivity increased to 6.2. Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) is a commercial polymer that is utilized for gas separation membranes. It has a relatively high free volume with high gas permeabilities but suffers from low gas selectivities. In this study, PPO polymers with number average molecular weights of 2000, 6000, 17,000, 19,000 and 22,000 were synthesized and blended with a poly(arylene ether ketone) synthesized from bisphenol A and difluorobenzophenone (BPA-PAEK) to make UV-crosslinkable films. The ketone and benzylic methylene groups on the BPA-PAEK and the PPO polymers respectively formed crosslinks upon exposure to broad wavelength UV light. The crosslinked blends had increased selectivities over their linear counterparts. DSC thermograms showed that the blends with all but the lowest molecular weight PPO had two Tg's, thus suggesting that two phases were present, one high in PBA-PAEK and the other high in PPO composition. The PBA-PAEK blend with the 2000 Mn PPO showed only one Tg between the two control polymers. Despite the immiscibility of these films, the gel fractions after UV exposure were high. Gel fractions as a function of the amount of the 22,000 Mn PPO were explored and did not show any significant change. UV spectroscopy of the individual components and the blends showed that more broad wavelength light was transmitted through the PPO component, so it was reasoned that films that was high in PPO composition crosslinked to deeper depths. The O2/N2 permeabilities and selectivities were measured for the linear and crosslinked films. Between the 33/67, 67/33, and 90/10 22k PPO/BPA PAEK crosslinked blended films, the 90/10 PPO/BPA PAEK gained the most selectivity and maintained a larger amount of its permeability. In comparison to commercial gas separation polymers, the non-crosslinked 33/67 22,000 Mn PPO/BPA PAEK blend outperformed polysulfone and cellulose acetate with a 2.45 degree of acetylation. Overall, we were able to blend a small amount of BPA PAEK with the commercially used PPO to create a mechanically robust crosslinked polymer film. / Ph. D.

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This thesis focuses on the synthesis and characterization of various poly(arylene ether)s to improve the efficiency of gas separation and water desalination membranes. This class of polymers includes polymers such as poly(arylene ether sulfone), poly(arylene ether ketone) and poly(phenylene oxide) which offer excellent thermal and mechanical stability and usually have high enough rigidity to support gas separation and water desalination operations. Besides the plethora of properties offered by the homopolymers, these polymers can also be post-modified to cater to specific needs. For example, the polyphenylene oxides have been brominated to increase the permeability for gas separation applications. Blending is another viable method to impart desirable properties to polymers. Bisphenol A based poly(arylene ether ketone) (BPAPAEK) has been blended with commercially available poly(2,6-dimethylphenylene oxide)s (PPO) of different molecular weights in a fixed ratio (66/34 wt/wt) and in various ratios of a 22000 g/mol PPO. All the blends were UV crosslinked to minimize plasticization by condensable gases and analyzed for gel fractions, whereas, only the 22,000 g/mol blends were tested for transport properties since they yielded the highest gel fractions and exhibited the best mechanical properties. The crosslinking reduced the free volume and improved the selectivity with some drop in permeability. The blends with 90% of the 22000 g/mol PPO by weight was plotted closest to the upperbound. A phosphine oxide based poly(arylene ether ketone) (POPAEK) was blended with the various PPOs in a similar manner. The results were compared to the BPAPAEK based blends in terms of miscibility behavior and transport properties. It was found that the POPAEK based blends had higher permeability due to the higher fractional free volumes of the POPAEK. The POPAEK was more compatible with the PPOs than BPAPAEK as seen by analyzing various blend permeability models, mechanical properties and scanning electron microscope images. Moreover, blends with both the PAEKs displayed only a small drop in mechanical properties, such as the Young's modulus and the yield strength in comparison to the parent polymers. Hydroquinone based poly(arylene ether sulfone) oligomers were synthesized, post-sulfonated and chemically crosslinked to determine the effect of water uptake, fixed charge concentration and block length of oligomers on the salt permeability and the hydrated mechanical properties of the networks. The sulfonic acid groups were placed strategically and quantitatively on the hydroquinone units. The strategic placement of the acid groups may help in maintaining high rejection of monovalent ions in the presence of divalent ions, as shown in unpublished work by our group. It was found that the water uptake and fixed charge density had the opposite effects on the salt permeability. Also, the salt permeability varied differently for 5000g/mol and 10000g/mol block based networks. Another polymer that was investigated in this thesis was poly(2-ethyl-2-oxazoline) (PEtOx). An elaborate account of synthesis of monofunctional, heterobifunctional and telechelic poly(2-ethyl-2-oxazoline)s using different initiators including methyl triflate, activated alkyl halides (e.g., benzyl halides), and non-activated alkyl halides has been presented in this thesis. Endgroup functionalities and molecular weight distributions were studied by SEC, 1H NMR and titrations. The oligomers initiated with the benzyl or xylyl chloride had a PDI of 1.3-1.4 which is broader than expected for a living cationic ring opened polymer. This was attributed to the participation of covalent species which propagated slowly in the activated halide reactions. These oligomers were quantitatively terminated as proven by NMR and titrations. Due to the molecular weight distributions and quantitative termination these oligomers were deemed to be desirable for drug delivery applications. / PHD / This work pivots around the synthesis and characterization of different classes of polymers which are long molecules made by joining small molecules. The structure-property relationships of different polymers with respect to applications such as gas separation, water desalination and drug delivery were examined. The first two projects were focused of gas separation applications. Gas separation is an essential process used to recover the required gas from a mixture of gases. This process is used in a number of industries such as natural gas, hydrogen recovery and air dehumidification. In these projects, gas separation membranes were used to remove non combustible components of natural gas such as carbon dioxide and hydrogen sulfide. Two different types of poly(arylene ether ketone)s (PAEKs) (a kind of polymer) were blended with a commercial polymer called poly(phenylene oxide) (PPO) and crosslinked at the surfaces to improve the gas transport properties of the commercial polymer. PPOs have high gas permeability and a low selectivity. In other words even though the PPO membranes would alow the gasses to pass through easily, the efficiency of gas separation would be low. The blending with the PAEKs improved the selectivity of the PPOs without much loss in throughput. These blends of the two different PAEKs were compared for transport and other relavent properties. It was found that the transport properties of the commercial polymer were improved markedly without much loss in mechanical properties which are usually sacrificed upon blending of two uncomaptible polymers. Water desalination applications were looked into for a polymer class called polysulfones. About 40% of the world’s population lives in water stressed areas. In order to address the water crisis, there is a need to look beyond primitive methods such as distillation which are inefficient. Hence, the polymeric membrane separations which do not involve phase change (eg liquid to gas and then back to liquid in distillation) were examined. The currently used polyamide membranes have a rough surface because of the way they are made, making them prone to deposition of salt and organic matter. This deposition makes them inefficient. They are also prone to degradation by chlorine. The polysulfones membranes have a smoother surface less prone to these depositions. Their resistance to chlorine makes them more viable for water desalination applications. The polysulfones were post modified to introduce charges to make them more suitable for water desalination purposes. The charges repelled the ions of same polarity and made the polymer more hydrophilic. However, as the number of charges increased, the water uptake of the polymer increased which resulted in a decrease in the effectiveness of salt /ion rejection. To increase the charge density of the polymers by (the effectiveness of ion rejection), the polymer chains were crosslinked at the ends. For deleniating the structure property relationships, the amount of charges were varied and two sets of chain lengths were studied. The salt permeability decreased with increase in fixed charge concentration and decrease in water uptake. Poly(2-Oxazolines), were investigated as potential drug delivery vehicles. Polymeric drug delivery vehicles have been used to control the rate of release of drugs in the body to avoid side effects. Another advantage of polymeric drug delivery systems is making the water insoluble drugs more compatible with the fluids in the body. Currently, polyethylene oxides are being used as drug delivery vehicles. However, these polymers have been known to produce antibodies in some people. In this work, poly(2-oxazolines) which are known to be more compatible with human body than PEOs were prepared using different initiators and end cappers to prepare an elaborate repertoire of controlled molecular weight and controlled functionality oligomers for further modification.