Semipermeable composite membrane

A process for producing a semipermeable composite membrane which comprises

• (a) treating a microporous substrate with a solution containing a soluble polymer containing at least 30 mole% of a recurring unit of formula (I) ##STR160## wherein Q represents an organic radical containing 2 to 30 carbon atoms and having a valence of (3+p) which optionally contains a heteroatom selected from the group consisting of oxygen, sulfur, nitrogen and halogen atoms;
• Y is bonded to the carbon atom in group Q and represents a direct bond, an alkylene group containing 1 to 3 carbon atoms or an unsubstituted or substituted phenylene group;
• Z represents ##STR161## R.sub.1 represents a hydrogen atom, or a monovalent organic radical containing 1 to 20 carbon atoms which may contain an amino group containing 1 to 2 active hydrogen atoms and a heteroatom selected from the group consisting of oxygen, nitrogen and halogen atoms;
• R.sub.2 represents an amino group containing 1 to 2 active hydrogen atoms or a monovalent organic radical containing 1 to 20 carbon atoms which contains at least one amino group containing 1 to 2 active hydrogen atoms and may contain a heteroatom selected from the group consisting of oxygen, nitrogen and halogen atoms;
• R.sub.1 and R.sub.2, together with the nitrogen atom to which they are bonded may represent a 5- to 18-membered nitrogen-containing heterocyclic ring which contains at least one amino group having one active hydrogen atom;
• when group Y represents a direct bond and group Z represents ##STR162## R.sub.1 may represent ##STR163## bonded to that carbon atom of the group Q which is bonded, either directly or through 1 or 2 carbon atoms, to the carbon atom to which the group Y is bonded;
• P is 0, 1 or 2;
• and
• when p is 1 or 2, L represents the group ##STR164## in which W represents a direct bond or an alkylene group containing 1 to 3 carbon atoms and Z, R.sub.1 and R.sub.2 are as defined above,
• (b) contacting the treated microporous substrate interfacially with a solution of a polyfunctional compound containing at least two functional groups capable of reacting with the amino group having one or two active hydrogen atoms, and
• (c) optionally heating them to form a thin film of the crosslinked polymer having semipermeability on one side of the microporous substrate.