Asymmetric, semipermeable membranes of cyclic polyureas

An asymmetric semipermeable membrane of a cyclic polyurea selected from the group consisting of a polyhydantoin of the formula

• and a polyparabanate of the formula ##STR16## wherein R.sup.1 and R.sup.2, when taken separately, are each selected from the group consisting of hydrogen, C.sub.1 to C.sub.6 alkyl and C.sub.3 to C.sub.6 cycloalkyl;
• R.sup.1 and R.sup.2, when taken together with the carbon atom to which they are attached, are cycloalkyl having 5 to 10 carbon atoms;
• R.sup.3 and R.sup.4 are each selected from the group consisting of C.sub.1 to C.sub.12 alkylene, C.sub.3 to C.sub.6 cycloalkylene, arylene and any two of the aforesaid members defining R.sup.3 and R.sup.4 connected together by a member selected from the group consisting of --O--, --CH.sub.2, ##STR17## --S--, --SO.sub.2 -- and --CO--;
• R.sup.5 is selected from the group consisting of a bond and the members of the group defining each of R.sup.3 and R.sup.4 ;
• X and Y are each selected from the group consisting of a bond, ##STR18## wherein R.sup.6 is selected from the group consisting of aryl, C.sub.1 to C.sub.12 hydroxyalkyl and C.sub.1 to C.sub.12 alkoxyalkyl and n is an integer from 2 to 200.