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.

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.