Ligand functionalized substrates with enhanced binding capacity

An article for biomaterial capture comprising

• (a) a porous polymeric membrane;
• and
• (b) grafted to said porous polymeric membrane, a polymer comprising interpolymerized units of at least one monomer consisting of (1) a terminal monovalent ethylenically unsaturated group, (2) at least one terminal monovalent ligand functional group selected from acidic groups, basic groups other than guanidino, and salts thereof, and (3) a multivalent spacer group that comprises at least one hydrogen bonding moiety and that is directly bonded to said terminal monovalent groups so as to link said terminal monovalent ethylenically unsaturated group and each said terminal monovalent ligand functional group by a chain of from 9 to 16 catenated atoms.