Permselective polymeric membrane prepared from polybenzimidazoles

A permselective polymeric membrane comprising a substrate polymer consisting essentially of a linear polymer containing as the main structural units N-aryl-substituted-benzimidazole units wherein said linear polymer;

• 1. is composed of the recurring units expressed by the following general formula (1)
• --A,B -- (1)
• wherein
• A is a divalent atomic group expressed by following general formula (2) ##EQU50## in which m and (n) are zero or 1, the two nitrogen atoms are bonded to two adjacent nuclear carbon atoms of the radical Ar.sub.1, and Ar.sub.2 is a monovalent aromatic group having up to 15 carbon atoms, and in which (i) when (n) is zero, Ar.sub.1 stands for a trivalent aromatic radical having up to 15 carbon atoms, Y is at least one member selected from the group consisting of -CONH-, -CONHNHCO-, -NHCONH- and ##EQU51## and when Y is -CONH- or ##EQU52## Ar.sub.1 may be bonded to either of the nitrogen and carbon atoms of Y;
• (ii) when (n) is 1, .sub.(n) indicates a single bond, Ar.sub.1 is a tetravalent aromatic radical having up to 15 carbon atoms, and Y is an atomic group expressed by following formula (3) ##EQU53## the two nitrogen atoms are bonded to the two adjacent nuclear carbon atoms of the aromatic radical Ar.sub.1, and Ar.sub.3 stands for a monovalent aromatic group having up to 15 carbon atoms;
• and (iii) the divalent atomic group expressed by above formula (2) is bonded in the polymer in either of the left and right directions;
• b. B stand for a single bond or a divalent organic radical in which the average number of atoms in the polymer exclusive of hydrogen atoms is not greater than 80 and carbon atoms are located at both the terminal ends, and when B is a single bond, the recurring unit A consists of the atomic group expressed by above formula (2);
• 2.