composite membranes that exhibit long - term resistance to biofouling comprise a porous support and a crosslinked polyamide discriminating layer having an external surface , the discriminating layer comprising a branched poly polymer attached to its external surface . the branched pao polymer typically has the structure of a molecular comb or brush , and is made by polymerization of a pao macromonomer of the following formula : ro — n — o ] m — v in which r is hydrogen or a c 1 - 20 aliphatic or aromatic group , v is any group containing a polymerizable site , each r ′ is independently hydrogen or a short chain alkyl group , n is an integer of 1 - 6 , and m is an integer of 1 to about 200 . the α end group can be either polymerized or copolymerized .