Hydrophobic interaction membrane adsorbers have been prepared using poly N-vinylcaprolactam as the binding ligand. The ligands were grafted using atom transfer radical polymerization. Binding and elution of lysozyme, bovine serum albumin, and IgG(4) was investigated. At high ionic strength during loading, the ligand is above its lower critical solution temperature and adopts a dehydrated conformation. During elution in low ionic strength buffer, the ligand is below its lower critical solution temperature and adopts a hydrated conformation. Use of a responsive ligand could lead to improved performance. The importance of tailoring the three-dimensional structure of the ligands is shown.