Semi-stiff chain aromatic polyamic-acids: New candidates for reverse osmosis membranes

Abstract

A series of polymers containing various amic-acid content have been prepared by the reaction of ether dianiline (EDA) with appropriate proportions of pyromellitic dianhydride (PMDA) trimellitoyl chloride (TMAC) and terephthaloyl chloride (TP) using low temperature polymerization techniques. The polymers have the following structures (corresponding to 50% amic-acid content): ▪ Homogeneous films were prepared by casting viscous polymer solutions (10–20% solid content) on glass plates and removing the solvent (DMAC) in a vacuum oven at room temperature. From reverse osmosis data with NaCl solutions at 5 MPa it can be seen that the water permeability increases with increasing carboxylic acid content, whereas the selectivity goes-through a maximum at 50% amic-acid content. The selectivity for different salt solutions increases in the order: CaCl 2 < NaCl < Na 2SO 4, showing typical cation exchange properties for the membranes. The influence of structural variations on the membrane properties have further been investigated using other monomers such as benzophenone tetracarboxylic acid dianhydride (BTDA) and sulfone ether diamines (SED) with different methyl substituents.