Semipermeable membranes

Semipermeable compound membranes consisting of at least one microporous substrate membrane and at least one semipermeable layer, wherein said semipermeable layer consists of a polymer material which has urazole structures and is the polycondensation product of at least one compound corresponding to the formula:

• ##STR5## and/or at least one water-soluble reaction product thereof, wherein R.sub.1 and R.sub.2, which may be the same or different or represent hydrogen or a C.sub.1 -C.sub.4 alkyl radical and R.sub.3 represent hydrogen, a C.sub.1 -C.sub.10 aliphatic radical and at least two of the radicals R.sub.1, R.sub.2 and R.sub.3 represent a radical corresponding to the formula ##STR6## in which R.sub.4, R.sub.5, R.sub.6 and R.sub.7, which may be the same or different independently of each other, represent hydrogen or a C.sub.1 -C.sub.4 alkyl radical, m represents an integer from 1 to 10 and n represents 1 or 2, or R.sub.1, R.sub.2 and R.sub.3 represent a glycidyl radical.