Permselective polymeric membranes of organic polyamide or polyhydrazide

A permselective polymeric membrane for use in desalination of saline water by reverse osmosis comprising contacting the saline water under pressure with a reverse osmosis membrane, consisting essentially of a synthetic organic polymer represented by the formula:

• ##EQU6## wherein:
• a. a, b, c, d, e, f, g, h, and i represent molar fraction (%) of each component, each of them being larger than zero or equal to zero, and satisfying the following relationship:
• a + b + c + d + e + f + g + h + i = 100
• a + c + d + e + f + g + h + i >
• 0
• a + b + c are equal to or greater than 20
• b. R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, and R.sub.6 are members selected from the group consisting of aromatic groups, heterocyclic groups and alicyclic groups having 4 to 30 carbon atoms,
• c. X.sub.1 is a group selected from the class consisting of --NHCO--, --CO--, and --CONHNHCO--, wherein, in the case of --CO--, it is bonded directly to a nitrogen atom in the heterocyclic ring in R.sub.1, R.sub.5, or R.sub.6,
• d. X.sub.2 is a group selected from the class consisting of --CONH--, --CO--, and --CONHNHCO--, wherein, in the case of --CO--, it is bonded directly to a nitrogen atom in the heterocyclic ring in R.sub.1, R.sub.5, or R.sub.6,
• e. Y is a group selected from the class consisting of --COOH--, SO.sub.3 H and carboxylic salts or sulfonic salts or alkali metals, alkaline earth metals, organic amine salts and mixtures thereof, and
• f. said membrane being asymmetric in thickness.