ABSTRACT.Temperature-responsive properties of surface-attached poly(N-isopropylacrylamide) (PNIPAM) network films with well-controlled chemistry are investigated. The synthesis consists in crosslinking and grafting preformed ene-reactive polymer chains through thiol-ene click chemistry. The formation of surface-attached and crosslinked polymer films has the advantage of being well-controlled without any caution of no-oxygen atmosphere or addition of initiators.PNIPAM hydrogel films with same crosslinks density are synthesized on a wide range of thickness, from nanometers to micrometers. The swelling-collapse transition with temperature is studied by using ellipsometry, neutron reflectivity and atomic force microscopy as complementary surface probing techniques. Sharp and high amplitude temperature-induced phase transition is observed for all submicrometric PNIPAM hydrogel films. For temperature above LCST, surface-attached PNIPAM hydrogels collapse similarly but without complete expulsion of water. For temperature below LCST, the swelling of PNIPAM hydrogels depends on the film thickness. It is shown that the swelling is strongly affected by the surface attachment for ultrathin films below approximately 150 nm. For thicker films above 150 nm (to micrometers), surface-attached polymer networks with same crosslinks density swell equally.The density profile of the hydrogel films in the direction normal to the substrate is confronted with in-plane topography of the free surface. It results that the free interface width is much larger than the roughness of the hydrogel film, suggesting pendant chains at the free surface.3