Composite membrane

1. A method of making a composite membrane comprising the steps of forming a discriminating layer having a thickness of less than 20 μm upon a surface of a porous support by sequentially applying immiscible coating solutions upon the support, wherein:

i) one coating solution comprises a crosslinking agent,

ii) one coating solution comprises a block copolymer, wherein the block copolymer comprises durable segments that include reactive pendent groups and sacrificial segments and wherein the weight ratio of durable to sacrificial segments is from 1:6 to 2:1,

iii) the reactive pendent groups react with the crosslinking agent to form a crosslinked matrix comprising micro-domains of the sacrificial segments, and

wherein said method comprises etching at least a portion of the sacrificial segments to yield pores having a mean flow pore size of from 0.1 to 0.001 μm.

2. The method of claim 1 wherein the crosslinking agent comprises a polyfunctional amine monomer.

3. The method of claim 1 wherein the sacrificial segments of the block copolymer comprise polylactic acid.

4. The method of claim 1 wherein the durable segments of the block copolymer comprise polystyrene.

5. The method of claim 1 wherein the reactive pendent groups of the block copolymer comprise at least one of: acyl halide, anhydride, epoxy and isocyanate.

6. The method of claim 1 wherein the discriminating layer comprises a crosslinked polyamide.

7. The method of claim 1 wherein the crosslinking agent includes a moiety selected from: isocyanates, alcohols, acids and amines.