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.

The results described in this dissertation focus on the synthesis and utilization of several disulfonated poly(arylene ether) random copolymer membranes in fuel cell and reverse osmosis applications. Poly(arylene ether)s were prepared by direct step copolymerization using a third monomer 3,3–-disulfonated 4,4–-dichlorodiphenylsulfone. The membrane properties of a 4,4–-biphenol-based disulfonated poly (arylene ether sulfone) random copolymer (BPS-35), optionally blended with various fluorine containing polymers or unsulfonated biphenol-based poly (arylene ether sulfone)s (Radel R) were investigated for fuel cell applications. Fluorine containing copolymers used included with 2,2–-hexafluoroisopropylidene 4,4–-biphenol based unsulfonated (6F-00) or disulfonated (6FS-35 and 6FS-60) PAES, hexafluoroisopropylidene biphenol based 4,4–-difluoro phenyl phosphine oxide) (6FPPO), and poly(vinylidene fluoride) (Kynar®). Tapping mode atomic force microscopy (TM-AFM) images of the membranes with 10 wt% of fluorinated copolymers showed macroscopic phase separation. Good miscibility between the copolymers at low concentrations was also confirmed by the observation of only one glass transition temperature. Compared to the benchmark Nafion 1135, the 10wt% blends of the fluorinated copolymers afforded a considerable reduction in the methanol permeabilities, which is important for direct methanol fuel cells (DMFC). The best DMFC performance with 0.5 M methanol fuel was illustrated with blends containing 10 wt% 6FS-00. At higher methanol concentrations (up to 2.0 M) BPS-35/6FS-00 (90/10) membranes outperformed both Nafion membranes. Blends of BPS-35 blends with 6FS-35 or Radel R were also used as RO membranes. The highest salt rejections of 97.2 and 98.0% were obtained from BPS35/Radel R (90:10) and BPS-35/6FS-35 (95:5) blends, respectively in the salt form. A systematic study of the preparation of BPS-20 random copolymer skin-core asymmetric membranes by diffusion induced phase separation (DIPS) from various polar aprotic solvent or cosolvent systems is reported. The best aprotic solvents to generate an asymmetric structure were NMP and DMAc whereas tetrahydrofuran (THF)/ formamide (FAm) (80/20 v/v) mixtures proved to be the best co-solvent systems. Acetone was the best non-solvent to prepare asymmetric membranes from both aprotic solvents and co-solvent mixtures. Overall, asymmetric membranes prepared from THF/FAm co-solvent mixtures illustrated the most stable phase separated morphology that was free of macrovoids. However, thicker skins (~5 μM) were formed due to the high volatility of THF. Therefore, ultra-thin skin thin film composites (TFC) based on BPS-20 in diethylene glycol (Di(EG) were prepared. Thermal treatment of these TFC was conducted at 90 °C and the addition of 20 wt% glycerin to the casting formulation helped to prevent pore collapse in the porous Udel polysulfone. A minimum of three coats was required to obtain a dense, smooth, and pinhole free skin layer. The generation of three dimensional (ternary) solubility parameter phase diagrams based on experimental data was formulated and a region of solubility based on the solubility parameters of the aprotic solvents and the different co-solvent systems was established for BPS-20. / Ph. D.

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.

Due to their outstanding properties, poly(arylene ethers) are useful as toughness modifiers in epoxy resins (EP). Furthermore, these polymers show rather low intrinsic fire risks. According to recent research it has been incorporated that poly(arylene ether phosphine oxides) [PAEPO’s] can further improve the fire behavior. Increasing phosphorous content of the PAEPO can influence the fire behavior too. Fire retardants containing phosphorus – regardless of whether an additive or reactive approach is used – show different mechanisms in the condensed and gas phase. In the present study PSU Control (BPA based polysulfone) with four different PAEPO’s and their corresponding blends with an EP were investigated. All poly(arylene ether phosphine oxides) were synthesized by nucleophilic aromatic polycondensation. The polymers obtained covered a wide range of weight average molar masses (6,000 – 150,000 g/mol) as determined by size exclusion chromatography with multi-angle light scattering detection (MALLS). FTIR, NMR spectroscopy and MALDI-TOF revealed formation of the desired polymer structure of the linear poly(arylene ethers). All polymers were easily soluble in common organic solvents, thus enabling processing from solution.The pyrolysis and the fire retardancy mechanisms of the polymers and blends with epoxy resin (EP) were tackled by means of a comprehensive thermal analysis (thermogravimetry (TG), TG-evolved gas analysis) and fire tests [PCFC, limiting oxygen index (LOI), UL-94, cone calorimeter]. The Mitsunobu reaction of Dimethyl-5-hydroxyisophthalate and a long chain semifluorinated alcohol requires triphenyl phosphine as a reactant. Identical, in some case higher yield was obtained in the usual conditions, with triphenyl phosphine and with trivalent phosphorus containing polymers, which was prepared in solvent free bulk (melt) polymerization technique from trivalent phosphorus monomer and a silylated diphenol in presence of CsF. Purification and the recovery of the final product which is always a big challenge in case of Mitsunobu reaction, was far more easier using polymer compared to triphenyl phosphine. During polymerization there was a possibility to have polymer having repeating unit containing both trivalent phosphorus and phosphine oxide. The trivalent phosphorus content of the polymer can be varied using different molar concentration of CsF.

Due to their outstanding properties, poly(arylene ethers) are useful as toughness modifiers in epoxy resins (EP). Furthermore, these polymers show rather low intrinsic fire risks. According to recent research it has been incorporated that poly(arylene ether phosphine oxides) [PAEPO’s] can further improve the fire behavior. Increasing phosphorous content of the PAEPO can influence the fire behavior too. Fire retardants containing phosphorus – regardless of whether an additive or reactive approach is used – show different mechanisms in the condensed and gas phase. In the present study PSU Control (BPA based polysulfone) with four different PAEPO’s and their corresponding blends with an EP were investigated. All poly(arylene ether phosphine oxides) were synthesized by nucleophilic aromatic polycondensation. The polymers obtained covered a wide range of weight average molar masses (6,000 – 150,000 g/mol) as determined by size exclusion chromatography with multi-angle light scattering detection (MALLS). FTIR, NMR spectroscopy and MALDI-TOF revealed formation of the desired polymer structure of the linear poly(arylene ethers). All polymers were easily soluble in common organic solvents, thus enabling processing from solution.The pyrolysis and the fire retardancy mechanisms of the polymers and blends with epoxy resin (EP) were tackled by means of a comprehensive thermal analysis (thermogravimetry (TG), TG-evolved gas analysis) and fire tests [PCFC, limiting oxygen index (LOI), UL-94, cone calorimeter]. The Mitsunobu reaction of Dimethyl-5-hydroxyisophthalate and a long chain semifluorinated alcohol requires triphenyl phosphine as a reactant. Identical, in some case higher yield was obtained in the usual conditions, with triphenyl phosphine and with trivalent phosphorus containing polymers, which was prepared in solvent free bulk (melt) polymerization technique from trivalent phosphorus monomer and a silylated diphenol in presence of CsF. Purification and the recovery of the final product which is always a big challenge in case of Mitsunobu reaction, was far more easier using polymer compared to triphenyl phosphine. During polymerization there was a possibility to have polymer having repeating unit containing both trivalent phosphorus and phosphine oxide. The trivalent phosphorus content of the polymer can be varied using different molar concentration of CsF.