Semipermeable composite membrane

A process for producing a sermipermeable composite membrane which comprises

• (a) crosslinking, on a microporous substrate or on a water solution, (i) a soluble polymer containing at least 30 mole % of a recurring unit of formula (I) ##STR89## wherein Y represents a direct bond, a methylene group, a carbonyl group of the formula ##STR90## or an unsubstituted or substituted phenylene group;
• 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 sulfur atoms;
• R.sub.2 represents a hydrogen atom, 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 sulfur 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 hetero-cyclic ring which contains at least one amino group having one active hydrogen atom;
• R.sub.3 represents an alkylene group containing 2 to 5 carbon atoms which may have an --OH group;
• and
• R.sub.4 represents a hydrogen atom or a methyl group, and having at least 0.5 milliequivalent, per gram of said polymer, of an amino group containing 1 or 2 active hydrogen atoms, with (ii) a polyfunctional compound containing at least two functional groups capable of reacting with the amino groups having one or two active hydrogen atoms, and
• (b) when the crosslinking reaction is carried out on a water solution, placing the thus formed membrane on a microporous substrate, and
• (c) optionally heating the membrane and substrate to ensure bonding thereof.