A new concept for the method to provide semipermeability in ultrathin and single-component wholly aromatic polyamide membranes has been developed for the first time. It was found that water molecules could permeate through the membrane prepared not from polyamides containing flexible ether, bulky binaphthyl, or fluorene rigid units, but one with carboxylic acid groups under a reverse osmosis mode. However, the enhancement of water transport properties by introducing the hydrophilic group of polyamide was not substantial. Therefore, polyamide membranes were prepared from the solution containing aqueous additives in order to weaken hydrogen bonds between polymer chains and thereby to suppress the aggregation of the polymer chains. As a result, water flux was dramatically improved with slightly improved NaCl rejection. Our analyses based on attenuated total reflectance Fourier transform infrared spectroscopy and solid-state carbon polarization and magic angle spinning nuclear magnetic resonance ( 13 C CPMAS NMR) spectroscopy confirmed that the aggregation of polymer chains due to the hydrogen bonds among the amide linkages was suppressed by the coordination of the aqueous additives to the amide linkage. The state of water in the membranes analyzed by differential scanning calorimetry also supported the formation of pores.

A series of polybenzimidazoles (PBIs) with different main chains and sulfonated PBI were successfully synthesized from the corresponding dicarboxylic acids and 3,3'-diaminobenzidine for the formation of ultrathin, single-component, and semipermeable membranes. Furthermore, the covalently crosslinked PBI membrane was prepared by the reaction of sulfonated PBI with divinyl sulfone. Their water transport properties were evaluated under a reverse osmosis mode and compared with the primary structure based on the water permeability (A) and salt permeability (B) values normalized by the membrane thickness. It was found that the A and B values of the PBIs were improved with increasing the weight ratio of the imidazole rings per repeating unit, the introduction of sulfonate group as the hydrophilic group to the PBI was an effective way to enhance the A value, and the crosslinked structure enhanced the salt rejection rate (R) value while maintaining the water flux.

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The synthesis, conformational preferences, hydrogen bonding behaviors, and membrane properties of new partially N‐methylated random aromatic copolyamides were reported. These copolyamides were prepared by the low temperature polycondensations of isophthaloyl chloride with 3,5‐diaminobenzoic acid, N,N'‐dimethyl‐4,4'‐diaminodiphenyl ether (MDAE), and 4,4'‐diaminodiphenyl ether. The incorporation of the N‐methyl amide linkages into the polymer backbone decreased the contents of the cis conformation in the N‐methyl amide linkages and suppressed the hydrogen bondings among the amide linkages. Furthermore, the surface hydrophilicity of the copolyamides evaluated by water contact angle measurements decreased with increasing the MDAE unit in the polymer backbone. These experimental results indicated that the suppression of the hydrogen bonding and the existence of the tertiary amide linkage in the cis conformation induced the loose packing of the polymer chains. As a result, the incorporation of the N‐methyl amide linkage increased water flux and decreased salt rejection. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 3453–3462

Front Cover: Aromatic random copolyamide membranes are prepared and characterized in article number https://doi.org/10.1002/macp.201700522 by Hidetoshi Matsumoto and co‐workers. The partial N‐methylation of the amide linkages suppresses hydrogen bonding between polymer chains. The size of the free volume elements can be tuned by controlling the intramolecular interaction between polymer chains, leading to improved transport properties through the membranes.