Multiblock copolymers of poly(2,5-benzophenone) and disulfonated poly(arylene ether sulfone) for proton-exchange membranes. I. Synthesis and characterization

Nanophase-separated, hydrophilic-hydrophobic multiblock copolymers are promising proton-exchange-membrane materials because of their ability to form various morphological structures that enhance transport. A series of poly(2,5-benzophenone)-activated, telechelic aryl fluoride oligomers with different block molecular weights were successfully synthesized by the Ni(0)-catalyzed coupling of 2,5-dichlorobenzophenone and the end-capping agent 4-chloro-4'-fluorobenzophenone. These telechelic oligomers (hydrophobic) were then copolymerized with phenoxide-terminated, disulfonated poly(arylene ether sulfone)s (hydrophilic) by nucleophilic, aromatic substitution to form hydrophilic-hydrophobic multiblock copolymers. High-molecular-weight multiblock copolymers with number-average block lengths ranging from 3000 to 10,000 g/mol were successfully synthesized. Two separate glass-transition temperatures were observed via differential scanning calorimetry in the transparent multiblock copolymer films when each block length was longer than 6000 g/mol. Tapping-mode atomic force microscopy also showed clear nanophase separation between the hydrophilic and hydrophobic domains and the influence of the block length as it increased from 6000 to 10,000 g/mol. Transparent and creasable films were solvent-cast and exhibited moderate proton conductivity and low water uptake. These copolymers are promising candidates for high-temperature proton-exchange membranes in fuel cells, which will be reported separately in part 11 of this series. (c) 2006 Wiley Periodicals, Inc.