This dissertation is aimed at understanding the microstructure evolution in styrene — diene block copolymer — based pressure-sensitive adhesive compositions in melt. The work also focuses on determining the microphase separation mechanism in adhesive melts containing various amounts of low molecular weight resin (tackifiers) blended with styrene — diene block copolymers. To understand the correlation between adhesive morphology and their dynamic mechanical behavior, small angle X-ray scattering (SAXS) and rheological analysis were performed on blends with different compositions. A modified Percus — Yevick model combined with Gaussian functions was used fit the liquid like disordered and bcc — ordered peaks of the SAXS intensity profiles. The morphological parameters derived from SAXS analysis corresponded to features such as the size and extent of ordering of the microphase separated polystyrene domains. The variation in these parameters with respect to temperature and adhesive composition correlated reasonably well with the trends observed in the shear modulus measured using rheological analysis. It was found that the ordering of polystyrene domains was influenced by the tackifier content in the adhesive blends. Polymer chain mobility was determined to be the dominant factor governing ordering kinetics, which depended on both the quench temperature and tackifier content in the blends. The addition of increasing amounts of tackifier eventually leads to a shift from a nucleation and growth type mechanism to a spinodal decomposition mechanism for phase separation and ordering. The compatibility of the tackifier with the polystyrene chains had a significant impact on the morphological transitions and microphase separation in adhesive blends. The blends containing a styrene — incompatible tackifier showed ordering over a broader range of temperatures compared to the blends containing a polystyrene — compatible tackifier. / Ph. D.

Linear thermoplastic polyesters are commonly used in high volume applications such as food containers, films and textile fibers. The physical and mechanical properties of these materials are well documented and are a function of chemical structure and morphology (e.g. semi-crystalline, amorphous, etc.). Polyesters, as are many organic polymers, are quite flammable. Polydimethylsiloxane homopolymer exhibits low mechanical strength and, even at high molecular weight, exists as a viscous fluid rubbery gum due to its low glass transition temperature of approximately -123°C. However, one of the many attractive properties of this polymer is its relatively low flammability and if properly designed, organic "sand-like" silicates are produced in oxidizing atmospheres at elevated temperatures (e.g. 500-700°C). This thesis discusses the synthesis and characterization of novel, high molecular weight cycloaliphatic and aromatic polyester/ poly(dimethylsiloxane) segmented copolymers. The cycloaliphatic copolymers were synthesized via a melt process using a high trans content 1,4 dimethylcyclohexanedicarboxylate, and 1,4 butanediol or cyclohexanedimethanol, while the partially aromatic systems were synthesized using dimethyl terephthalate and butanediol. Primary and secondary aminopropyl terminated poly(dimethylsiloxane) oligomers of controlled molecular weight were endcapped with excess diester to form an amide linked diester terminated oligomer. The latter was then incorporated into the copolymer via melt transesterification to afford a multiphase segmented copolymer. Selected compositions showed enhanced ductility and hydrophobic surface modification. The polysiloxane segment was effeciently incorporated into the copolymers and was unaffected by the transesterification catalyst under typical reaction conditions. The homopolymers and copolymers were characterized by solution, thermal, and mechanical, and surface techniques. The segmented copolymers were demonstrated to be microphase separated as determined by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and transmission electron microscopy. The surface of the copolymers was enriched with the polysiloxane segment as evidenced by contact angle analysis. Thermal gravimetric analysis of the segmented copolymers containing identical amounts of PDMS, but varying in the primary or secondary nature of their amide linkages, exhibited quantitatively identical char yields and weight loss behavior. The segmented copolymers exhibited char yields in air superior to those of their respective homopolymers. Additionally, aromatic poly(tetramethyleneoxide) (PTMO) based polyether/polyester segmented copolymers were modified with poly(dimethylsiloxane). DMA revealed an apparent shift (higher Tg) of the PTMO segment reflecting an increase in phase mixing with the "hard" polyester segment, possibly induced by the hydrophobic PDMS phase. / Master of Science

This thesis addresses the systematic modification of poly(tetramethylene oxide) (PTMO), polyether based segmented thermoplastic polyurethane with a secondary aminoalkyl functional polydimethylsiloxane (PDMS), which was intended to improve the fire resistance of polyurethane systems. The PDMS oligomer was successfully incorporated into the polyurethane backbone via one step solution polymerization. The effect of PDMS content on thermal stability, morphology, surface composition, mechanical properties, and fire resistance of polyurethane was investigated. These polymers displayed a complex two phase morphology and composition-dependant mechanical properties. The PDMS segment microphase separated from other polyurethane segments and varying microphase separation morphologies were observed with differing PDMS content. Spherical dispersed complex phases and co-continuous phases occurred when the PDMS content was 15wt% and 55wt%, respectively. Similar thermal stability was observed for both the polyurethane control and the PDMS modified polyurethanes, but the later displayed increased char yield in air with increased PDMS concentration. Quantitative measurements of the fire resistance of the modified polyurethanes by cone calorimetry showed that the peak heat release rate of the 15wt% siloxane modified samples dropped 67wt%, compared with the polyurethane control. However, the peak heat release rate did not further change with increasing siloxane content. Excellent mechanical properties, in terms of tensile strength and elongation, were found for the modified polyurethane with 15wt% of PDMS. Higher PDMS levels did reduce tensile strength, probably because of the reduction in strain crystallizing PTMO content. The PDMS modification, which resulted in improved fire resistance and excellent mechanical properties, is attributed to the low surface energy of the PDMS segment that tended to migrate to the surface of the polymer. It could be oxidized into a partially silicate-like material upon heating in air. In addition, the syntheses of primary and secondary aminoalkyl functional PDMS based segmented polyureas are described herein. Two-phase morphology was observed for all the polyurea samples, even when the hard segment concentration was as low as 6wt%. All these polyureas formed clear transparent films that exhibited good mechanical properties even with very high PDMS content, up to 94wt%. They also demonstrated similar thermal stability, independent of the PDMS end group. However, the nature of the end group, i.e. primary or secondary aminoalkyl, had a dramatic effect on mechanical and morphological properties of these PDMS based polyureas, which was interpreted in terms of the level of hydrogen bonding. / Ph. D.

Stimuli responsive polymers (SRP) have attracted a lot of attention, due to their potential and promising applications in many fields, as protein-ligand recognition, on-off switches for modulated drug delivery or artificial organs. Poly(N-isopropylacrylamide) (PNIPAM) is one of the most widely studied polymers due to its lower critical solution temperature (LCST) at ~ 32° C in aqueous solution. Additionally, glycopolymers, where free sugar units are present, have potentially interesting applications especially in bio-recognition where sugars play an important role. In this work, our interest was focused on the synthesis of glycomonomers and its block- and random- copolymers with NIPAM. NIPAM homopolymers with an active chain transfer unit at the chain end could be prepared by RAFT. They were used as macro-chain transfer agents to prepare a variety of sugar containing responsive block copolymers from new glycomonomers by the monomer addition concept. The LCSTs of the aqueous solutions of the copolymers are affected strongly by the comonomer content, spacer chain length of the glycomonomer and the chain architecture of the copolymers. These polymers were coated on a solid substrate by spin coating and crosslinked by plasma immobilization. Characterization of the polymers was performed by nuclear magnetic resonance spectroscopy (NMR), ultraviolet (UV), dynamic light scattering (DLS, detection of aggregation behaviour) and gel permeation chromatography (GPC). Polymer films were investigated by ellipsometry, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) regarding their surface properties. Afterwards sulfation of sugar – OH groups was performed in order to obtain heparin like structure, as heparin exhibits numerous important biological activities, like good interaction with diverse proteins. Finally, affinity of the polymers (sulfated and non sulfated form) on a solid support to the endothelial cells was investigated.

Les méta-matériaux offrent la possibilité d'obtenir des propriétés physiques nettement améliorées en comparaison avec celles des matériaux naturels. Dans ce travail, nous explorons une nouvelle variété de métamatériaux thermoélectriques à base de micro-et nano-structuration du silicium, sous la forme de super-réseaux verticaux, avec comme visée applicative la récupération d'énergie thermique ainsi que le refroidissement. En outre, nous focalisons nos efforts sur une méthodologie expérimentale permettant la réalisation de ces matériaux par des moyens simples et peu coûteux. La première partie de cette thèse sert d'introduction aux phénomènes thermiques qui constituent la base de la conduction électrique et de la dissipation de chaleur dans les nanostructures, respectivement par émission thermo-ionique et par la diffusion de phonons. Cette partie détaille également les principes et résultats de caractérisation thermique à l'aide des méthodes 3ω et 2ω. La deuxième partie de cette thèse décrit les approches de micro- nanostructuration descendante « top-down » et ascendante « bottom-up », en vue de la fabrication de super-réseaux nanométriques sur du silicium mono-cristallin. La nouvelle architecture verticale proposée soulève des défis technologiques qui sont traités à travers l'exploration de techniques expérimentales originales pour produire, d'une manière efficace et sur de grandes surfaces, des structures submicroniques à fort facteur de forme. Ces techniques comprennent l'utilisation de motifs résultant de lithographie traditionnelle combinée à l'extrusion pour en produire des structures volumiques. En outre, l'utilisation de nanofibres et de diblocs copolymères comme nano-motifs géométriques sont également présentés pour nous rapprocher davantage de l'objectif ultime du projet / Metamaterials offer the benefit of obtaining improved physical properties over natural materials. In this work, we explore a new variety of thermoelectric metamaterials based on silicon micro- and nano- structuration, in the form of vertical superlattices for use in energy-related applications. Additionally, we focus on a route towards fabricating these materials using simple and low-cost means compared to prior attempts. The first part of this thesis serves as an introduction to the thermal phenomena which form the basis for electrical conduction and heat dissipation by thermionic emission and phonon scattering at the nanoscale. These principles forms the crux of the device. This section also details the characterization principles and results using the 3ω and 2ω methods for thermal measurement. The second part of this thesis describes both top-down and bottom-up approaches towards fabricating nanoscale superlattices from single-crystalline silicon. The novel proposed vertical architecture raised technological challenges that were tackled through the exploration of original experimental techniques for producing high aspect ratio (HAR) structures in an effective manner and over large surface areas. These techniques include the use of traditional lithography patterning and subsequent extrusion of volumic structures. Additionally, the use of nanofibers and diblock copolymers as templates for further etching of HAR silicon nanostructures are also presented to bring us closer to the ultimate goal of the project

A series of modified poly(arylene ether sulfone)s (PAES) incorporating hexafluoroisopropylidene units and co-monomers, bisphenol A (BA), 4,4′-dihydroxyterphenyl (DHTP) and triptycene-1,4-hydroquinone (TPDH), were synthesized using a polyetherification synthetic method. These thermoplastic PAES were copolymerized with the elastomer, polydimethylsiloxane (PDMS) to form segmented block copolymers. The segmented block copolymers with diverse PAES structures were studied and investigated for their thermal, tensile, and morphological properties. These multiphase segmented block copolymer materials have the potential to impart useful combinations of optical transparency, thermal stability, and enhanced tensile properties, and enhanced environmentally resistant properties for various high impact, high performance applications. In Chapter 2, hexafluoroisopropylidene bisphenol PAES (BAF PAES) segmented block copolymers containing various volume fraction of PDMS were synthesized. Analysis of the segmented block copolymer films by atomic force microscopy (AFM) and small angle x-ray scattering (SAXS) show the materials are microphase separated. Further analysis of the BAF PAES segmented block copolymers by transmission electron microscopy (TEM) show an increased morphological order with decreasing PDMS content, with lamellar morphologies formed at higher or near equal PAES and PDMS volume fractions. Comparatively, the morphological properties of the BAF PAES segmented block copolymers are considerably different from the isopropylidene bisphenol PAES (BA PAES) segmented block copolymer of similar PDMS volume percents. In this document, segmented block copolymers prepared from BA PAES incorporating 4,4′-dihydroxyterphenyl (DHTP) and triptycene-1,4-hydroquinone (TPDH) co-monomers were characterized by proton nuclear magnetic resonance spectroscopy (¹H NMR). Films of these materials, prepared from THF solution, were tested for thermal and tensile properties. These materials provide higher thermal stabilities over the BA PAES segmented block copolymers with thermal degradation ranging 380–435 °C under nitrogen at 5%-wt. loss. Similarly, the PAES incorporating co-monomers gave higher Tg (200 °C) than the BA PAES (183 °C) synthesized in our labs. Previously synthesized BA PAES segmented block copolymers showed plastic to elastomeric tensile properties upon increasing addition of PDMS content. These new segmented block copolymers, incorporating co-monomers, provided comparable results with the reported BA PAES segmented block copolymers analogues. The last research topic discussed in this dissertation covers the preparation of blends from 5% of segmented block copolymer and 95% of Udel®, donated by Solvay Advanced Polymers. The preparation of blends from the segmented block copolymers containing random copolymers led to materials with higher moduli than Udel® as observed by dynamic mechanical analysis (DMA). Tensile measurements performed by Instron also show the blends have high moduli, though no changes in the tensile elongation comparable to Udel®. / Ph. D.

The potential success of a proton exchange membrane (PEM) fuel cell as an alternative energy source depends highly upon the development of high performance PEMs. Typically, state-of-the-art PEMs have been perfluorinated sulfonated ionomer membranes such as Nafion® by DuPont. Although these membranes demonstrate good mechanical and electrochemical properties under moderate operating conditions (e.g., < 80 ºC), their performance at high temperature (e.g., > 80 ºC) and low relative humidity (RH) drastically deteriorates. To overcome these problems, PEM materials with enhanced properties are essential. Recently, the McGrath group has shown that PEM materials with hydrophilic-hydrophobic segments can significantly improve proton conductivity under low RH by forming enhanced hydrophilic domain connectivity. In this dissultation, novel multiblock copolymers based on disulfonated hydrophilic-hydrophobic multiblocks were synthesized and investigated for their potential application as PEMs. The relationship between copolymer chemical composition and resulting properties was probed with a variety of hydrophilic and hydrophobic segments. Most multiblock copolymers in this research were developed with fully disulfonated poly(arylene ether sulfone) (BPS100) as the hydrophilic segment, and various high performance polymers including polyimides, poly(arylene ether sulfone)s, and poly(arylene ether ketone)s as the hydrophobic segment. Ionic groups on the hydrophilic blocks act as proton conducting sites, while the non-ionic hydrophobic segments provide mechanical and dimensional stability. The correlation between the fuel cell performances and the hydrophilic-hydrophobic sequences was also evaluated. The morphological structures of the multiblock copolymers were investigated using tapping mode atomic force microscopy (TM-AFM), transmission electron microscopy (TEM), and dynamic mechanical analysis (DMA). The experiments demonstrated a well-defined nanophase separated morphology. Moreover, changes in block length had a pronounced effect on the development of phase separated morphology of the system. Proton conductivity measurements elucidated the transport process in the system, with the multiblock copolymers demonstrating higher conductivities compared to Nafion and random copolymer systems with similar ion exchange capacity (IEC) values. The new materials are strong candidates for use in PEM systems. / Ph. D.

Sulfonated poly(arylene ether sulfone)s can exhibit several ideal features as potential desalination membranes for reverse osmosis applications, including chlorine resistance, low surface fouling, and high water flux. However, this class of polymer membranes has suffered from two major drawbacks that jeopardize effective levels of salt rejection in order to achieve high water flux. In mixed salt feed sources, monovalent salt rejection decreases when divalent cations such as Ca2+ bind with the anionic sulfonate groups to cause charge screening, and this can lead to too much salt passage for the membranes to be competitive with interfacially produced polyamides. Sulfonate fixed charge concentration must be high enough for sufficient membrane water uptake to obtain high membrane water flux, but if the water uptake is too high, this permits increased salt passage. The research described in this dissertation attempts to address both of these challenges through the design of a sulfonated monomer that strategically spaces the ionic groups along the polymer backbone chains to inhibit divalent ion binding. Free radical crosslinking further tunes the hydrated free volume in the RO membranes. A mono-sulfonated comonomer, sodium 3-sulfonate-4,4'-dichlorodiphenylsulfone (ms-DCDPS), was synthesized by stoichiometrically controlled electrophilic aromatic sulfonation of 4,4'-dichlorodiphenylsulfone (DCDPS). HPLC-UV revealed complete isolation of ms-DCDPS free of by-products after the 1st recrystallization and 1H NMR analysis confirmed the structure. A standard calibration curve was developed to accurately determine the leftover quantity of excess NaCl that was used for precipitation during the work-up procedures. A series of linear sulfonated poly(arylene ether sulfone)s with varying ms-DCDPS incorporation was synthesized. 1H NMR confirmed the structure of the polymers and size-exclusion chromatography confirmed that the intended molecular weights were achieved. The copolymers were cast into dense films and the mechanical and transport properties were measured in their fully hydrated states. Tensile tests revealed mechanically robust, tough membranes with glassy elastic moduli and high strains at break. The dense membrane prepared from sulfonated poly(arylene ether sulfone) with 51% of the repeat units sulfonated had NaCl rejection = 99.3% measured at 400 psi and 2000 ppm NaCl with a water permeability coefficient of 0.57 x 10-6 cm2/s. The salt rejection remained greater than 99% when a mixed salt feed source containing Ca2+ in the 0-200 ppm range together with the 2000 ppm NaCl was introduced. Crosslinked mono-sulfonated oligomers were synthesized with targeted molecular weights by utilizing stoichiometric quantities of monomers with the desired degrees of sulfonation, and the endgroups were functionalized with tetrafluorostryene. These end-functionalized sulfonated oligomers were crosslinked by both thermal and UV free radical methods in the presence of initiators without any additional crosslinking agents. Reaction conditions were thoroughly investigated and optimized to produce highly crosslinked membranes that yielded gel fractions greater than 87%, as measured by solvent extraction in dimethylacetamide. The hydrated crosslinked membranes were tested for both mechanical and transport properties, and the results were compared to their linear membrane counterparts. Crosslinking decreased the hydrated free volume and reduced water uptakes when compared to linear sulfonated membranes. Tensile tests of the fully hydrated crosslinked membranes showed good mechanical properties. The transport properties of a dense UV crosslinked membrane prepared with a 10,000 g/mol oligomer having 50% of the repeat units sulfonated was tested under RO cross-flow conditions at 400 psi and 2000 ppm NaCl in the feed. The membrane demonstrated a salt rejection = 98.4% with a water permeability coefficient of 0.49 x 10-6 cm2/s. / Doctor of Philosophy / Billions of individuals across the world lack clean, affordable drinking water, and the unavailability of fresh drinking water can be attributed to both physical and economic reasons. Several techniques have been utilized to produce potable water for human consumption that include both water desalination and recycling procedures. Water desalination is a process that allows for purifying salt contaminated water into drinking water. The two major desalination processes involve either distillation or passage through polymer membranes. Distillation separates water from salt by heating liquid water to form a gas, and collecting the vapor as condensate while impurities remain in the heated bulk material. Polymer membranes separate impurities through filtration where membranes allow water to pass through a physical barrier while rejecting the unwanted contaminants, including salt. Reverse osmosis desalination is the most common membrane separation process. Reverse osmosis membranes are comprised of either short-chain crosslinked oligomers or long-chain linear polymers. Commercial reverse osmosis membranes are largely poly(amide)s where a thin film is formed in an interfacial reaction. The membranes allow for almost quantitative salt rejection with high water fluxes. But, these membranes degrade over time from periodic cleaning with chlorine disinfectants. This dissertation primarily focuses on the implementation of an alternative polymer membrane material known as a mono-sulfonated polysulfone that strategically distributes the fixed sulfonate charged groups along the polymer backbone. Theses reverse osmosis mono-sulfonated polysulfones display comparable salt rejection with better chemical resistance than commercial poly(amide)-based membranes, and could potentially offer a replacement in the market.

This thesis research focused on the synthesis and characterization of disulfonated poly(arylene ether sulfone) hydrophilic-hydrophobic segmented and multiblock copolymers for application as proton exchange membranes (PEMs) in fuel cells or as reverse osmosis (RO) membranes for water desalination. The first objective was to demonstrate that synthesizing blocky copolymers using a one oligomer, two monomer segmented copolymerization afforded copolymers with similar properties to those which used a previous approach of coupling two preformed oligomers. A 4,4′-biphenol based hydrophilic block of disulfonated poly(arylene ether sulfone) oligomer of controlled number average molecular weight (Mn) with phenoxide reactive end groups was first synthesized and isolated. It was then reacted with a calculated amount of hydrophobic monomers, forming that block in-situ. Copolymer and membrane properties, such as intrinsic viscosity, tensile strength, water uptake, and proton conductivity, were consistent with those of multiblock copolymers synthesized via the oligomer-oligomer approach. The segmented polymerization technique was then used to synthesize a variety of other copolymers for PEM applications. The well known bisphenol phenolphthalein was explored as a comonomer for either the hydrophilic and hydrophobic blocks of the copolymer. Membrane properties were explored as a function of block length for both series of copolymers. Both series showed that as block length increases, proton conductivity increases across the entire range of relative humidity (30-100%), as does, water uptake. This was consistent with earlier research which showed that the water self-diffusion coefficient scaled with block length. Copolymers produced with phenolphthalein had higher tensile strength, but lower ultimate elongation than the 4,4′-biphenol based copolymers. Multiblock copolymers were also synthesized and characterized to assess their feasibility as RO membranes. A new series of multiblock copolymers was synthesized by coupling hydrophilic disulfonated poly(arylene ether sulfone) (BisAS100) oligomer with hydrophobic unsulfonated poly(arylene ether sulfone) (BisAS0) oligomer. Both oligomers were derived using 4,´-isopropylidenediphenol (Bis-A) as the bisphenol. Phenoxide-terminated BisAS100 was end-capped with decafluorobiphenyl and reacted at relatively low temperatures (~ 100 oC) with phenoxide-terminated BisAS0. Basic properties were characterized as a function of block length. The initial membrane characterization suggested these copolymers may be suitable candidates for reverse osmosis applications, and water and salt permeability testing should be conducted to determine desalination properties. The latter measurements are being conducted at the University of Texas, Austin and will be reported separately. / Ph. D.

Sulfonated poly(arylene ether sulfone)s as ion conductive copolymers have numerous potential applications. Membranes cast from these copolymers are desirable due to their good chemical and thermal stability, excellent mechanical strength, satisfactory conductivity, and excellent transport properties of water and ions. These copolymers can be used in a variety of topologies. Structure-property-performance relationships of these membranes as candidates for electrolysis of water for hydrogen production and for purification of water from dissolved ions have been studied. Linear and multiblock sulfonated poly(arylene ether sulfone)s are potential alternative candidates to Nafion membranes for hydrogen gas production via electrolysis of water. In this investigation, these copolymers were prepared from the direct polymerization of di-sulfonated and non-sulfonated comonomers with bisphenol monomers. In systematic investigations, a series of copolymers with modified properties were synthesized and characterized by changing the ratio of the sulfonated/non-sulfonated comonomers in each reaction. These copolymers were investigated in terms of mechanical stability, proton conductivity and H2 gas permeability at a range of temperatures and under fully hydrated conditions. A multiblock copolymer was synthesized and evaluated for its potential as membranes for electrolysis of water and for fuel cell applications. The multiblock copolymer contained some fluorinated repeat units in the hydrophobic blocks, and these were coupled with a fully disulfonated hydrophilic block prepared from 3,3'-disulfonate-4,4'-dichlorodiphenyl sulfone and biphenol. After annealing, the multiblock copolymer showed enhanced proton conductivity and a more ordered morphology in comparison to the random copolymer counterparts. At 90 oC and under fully hydrated conditions, improved proton conductivity and controlled H2 gas permeability was observed. Finally, the performance of the multiblock copolymer, which was measured as the ratio of proton conductivity to H2 gas permeability, was improved when compared to the state-of-the-art membrane, Nafion 212, by a factor of 3. In another systematic study, two series of random copolymers were synthesized and characterized, and then cast into membranes to evaluate for electrolysis of water. One series contained solely hydroquinone as the phenolic monomer, while the second series contained a mixture of resorcinol and hydroquinone as phenolic comonomers. The polymers that contained only the hydroquinone monomer showed exceptionally good mechanical properties due to the para-substituted comonomer in the composition of the polymer. In the resorcinol-hydroquinone series, gas permeability was constrained due to the presence of 25% of the meta-substituted comonomer incorporated into its structure. Low gas permeability and high proton conductivity at elevated temperatures were obtained for both the linear random and multiblock copolymers. Performance of these copolymers was superior to Nafion at elevated temperatures (80-95°C). In order to enhance the durability of these materials in their hydrated states at elevated temperatures, the surfaces of these copolymer films were treated with fluorine gas. In comparison with pristine non-fluorinated membranes, the modified membranes showed decreased water uptake and longer durability in Fenton's reagent. A series of linear and crosslinked copolymers were investigated with respect to their potential for use as membranes for desalination of water by electrodialysis and reverse osmosis. The crosslinked membranes were prepared by reacting controlled molecular weight, disulfonated oligomers that were terminated with meta-aminophenol with an epoxy reagent. The oligomers had systematically varied degrees of disulfonation and either 5000 or 10,000 Da controlled molecular weights. Membrane casting conditions were established to fabricate highly crosslinked systems with greater than 90% gel fractions. At such a high gel fraction, the water uptake of the crosslinked membranes was lower than that of the linear biphenol-based, disulfonated random copolymer with a similar IEC. Among these series of copolymers, it was shown that the crosslinked membranes cast from the oligomers with 50% degree of disulfonation and a molecular weight of 10,000 Da had the lowest salt permeability of 10-8 cm2/sec. For desalination applications, a comonomer was synthesized with one sulfonate substituent on 4,4'-dichlorodiphenyl sulfone. This new monosulfonated comonomer allows for even distribution of the ions on the linear copolymer backbone, and this may be important for controlling ion transport. Mechanical tests were conducted on the membranes while they were submerged in a water bath. The ultimate strength of a fully hydrated copolymer with an IEC of 1.36 meq/g was approximately 60 MPa with an elongation at break of 160%. Moreover, in a monovalent/divalent mixed salt solution, the monosulfonated linear copolymer exhibited a constant Na+ passage of less than 1.0%. / Ph. D. / Purification systems have become an increasingly important scientific and technological need for millions around who face water shortages and/or impure sources of potable water. In response, water purification and hydrogen gas production have been widely used to produce pure products from a variety of water sources. In general, current state-of-the-art methods in separation technologies feature two major drawbacks: they are energy intensive and costly processes. In response to the growing need for purified water or pure hydrogen gas for energy generation, polymeric materials are increasingly used in the form of membranes to produce a purer product and overcome the hindrances associated with current energy intensive and inefficient methods. These membranes serve as a barrier for unwanted species, while at the same time allowing the desired species to pass through. Under proper conditions, these purification or chemical processes would generate pure materials that can be used on demand. The chemistry of candidate polymeric materials is extremely important to design a membrane with desired properties. Therefore, the principal goals of this investigation were to synthesize polymers for use as membranes in three areas: 1) Electrolysis of water for ultra-pure hydrogen gas generation 2) Fuel cells applications for electricity generation, and 3) Desalination of water to provide drinking water. For each technology, a series of sulfonated poly(arylene ether sulfone) copolymers were synthesized and characterized. By applying different monomers or chemistries, a range of appropriate copolymers were synthesized whose characteristics varied in topology and architecture, depending on the desired application. Once these copolymers were synthesized, they were cast into membranes under proper established conditions. In addition, the structure-property-performance relationship of these sulfonated polysulfone membranes were further investigated to provide a direction for future studies.