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Abstract:
For more than ten years, polymers such as cellulose acetate and, more recently, polyamides or polyamidhydrazides have been used as materials for hyperfiltration membranes. Membranes prepared from some aromatic and heterocyclic or cycloaliphatic polymers with a rigid polymer backbone such as pyrrones, polybenzimidazoles, or polypiperazinamides also exhibit high salt rejection combined with high water permeability. These recent relate to a hypothesis which we used as a basis for membrane preparation from new polymers which should lead to optimal desalting properties. By analyzing the relationship between polymer molecular structure and desalination performance, polymers were selected with a low chain flexibility and a sequence of proton donator and acceptor groups along the polymer backbone which should promote the diffusion of water molecules without extensive immobilizing interaction. Low chain flexibility and suitable polarity were afforded by the polyamic acids and polyimides and therefore these polymers were selected for the exploratory preparation of efficient desalting membranes. Their regular structure also facilitates interpretation of the influence of the chemical and physical structural features of the polymer on water and salt permeability.
In addition, these polymers were already extensively studied as heat resistant materials which facilitates the extraction of related data concerning chain rigidity, polarity, and other relevant physico-chemical features from the literature. These data, combined with, for example, spectroscopic measurements made in these laboratories were used for comparison and analysis of the synthetized polymers. The results of hyperfiltration experiments with the various membranes were correlated with these independently characterized structural features.
