Preparation And Modification Of Sulfonated Poly(Arylene Ether Sulfone)s For Proton Exchange Membrane Applications

Proton exchange membrane fuel cells (PEMFC), due to their high efficiency and environmental friendship, have become a focal point of current research of new energy. One of the important components in a PEMFC is the proton exchange membrane (PEM), which decided the operation performance of fuel cells.This thesis focused on the development of SPAES-based proton exchange membranes, modification methods such as blending and cross-linking were used to enhance properties of membranes. Properties such as water uptake, ion exchange capacity, dimensional change, water stability, mechanical property as well as proton conductivity were investigated in detail.Phenoxide terminated hydrophilic oligomers were synthesized from 9,9’-bis(4-hydroxyphenyl) fluorine (BHPF) and 4,4’-difluorodiphenyl sulfone (DFDPS), then reacted with decafluorobiphenyl (DFBP) and further sulfonated by fuming sulfonic acid. A phenoxide terminated hydrophobic oligomer was synthesized from 4,4’-biphenol (BP) and 4,4’-difluorodiphenyl sulfone (DFDPS), then was reacted with decafluorobiphenyl (DFBP) to get the fluoro-terminated hydrophobic oligmer. A series of multiblock copolymers based on novel sulfonated poly (arylene ether sulfone) (bSPAES-SF) with highly rigid hydrophilic sulfonate blocks and flexible hydrophobic blocks were successfully synthesized by the condensation of the sulfonated decafluorobiphenyl (DFBP)-terminated telechelic oligomers and the hydroxyl-terminated telechelic oligomers. The bSPAES-SF membranes with IEC of 1.16-2.09 mmol/g exhibited exhibited high proton conductivity, hydrolytic and dimensional stability, The membrane of bSPAES-SF(5/10)-60 (2.09 mmol/g) showed proton conductivity of 182 mS/cm and dimensional change of 12.4%(in plane) and 16.6%(through plane) in water at 30℃, respectively.A series of bSPAES-SF/SPI blend membranes were obtained from bSPAES-SF and SPI (NTDA-BAPBDS/BAPB) by adjusting their mass ratios. The results show that these two polymers have good compatibility, transparent and uniform surface was observed for the membranes. By the introduction of SPI, the blend membranes displayed lower water uptake, enhanced mechanical property and dimensional stability compared to the pristine bSPAES-SF membranes. The blend membranes showed higher proton conductivity and water stability than the SPI membranes. The proton conductivity was in the range of 136-191 mS/cm. Weight losses no more than 7.1% were found for the blend membranes.The main chain copolymers were synthesized from DFBP and HFBPA. A phenoxide terminated hydrophilic oligomer was synthesized from BP and SDFPDS, and subsequently used as the starting materials to obtain graft-crosslinked membranes as PEMs. The titration IEC is very close to the calculated IEC value, indicating a completely crosslinking reaction. The graft-crosslinked membranes displayed excellent dimensional and water stability. The in plane and through plane dimensional change were in the range of 12.4% and 16.6%, respectively. Weight losses no more than 1.3% were found for the graft-crosslinked membranes. The proton conductivities are closely related to the IEC values and the hydrophilic segment length under the same testing conditions. Membrane with longer hydrophilic segment length exhibited higher proton conductivities.