Temperature-responsiveproperties of surface-attached poly(N-isopropylacrylamide)(PNIPAM) network films with well-controlledchemistry are investigated. The synthesis consists of cross-linkingand grafting preformed ene-reactive polymer chains through thiol–eneclick chemistry. The formation of surface-attached and cross-linkedpolymer films has the advantage of being well-controlled without anycaution of no-oxygen atmosphere or addition of initiators. PNIPAMhydrogel films with same cross-link density are synthesized on a widerange of thickness, from nanometers to micrometers. The swelling-collapsetransition with temperature is studied by using ellipsometry, neutronreflectivity, and atomic force microscopy as complementary surface-probingtechniques. Sharp and high amplitude temperature-induced phase transitionis observed for all submicrometric PNIPAM hydrogel films. For temperatureabove LCST, surface-attached PNIPAM hydrogels collapse similarly butwithout complete expulsion of water. For temperature below LCST, theswelling of PNIPAM hydrogels depends on the film thickness. It isshown that the swelling is strongly affected by the surface attachmentfor ultrathin films below ∼150 nm. For thicker films above150 nm (to micrometers), surface-attached polymer networks with thesame cross-link density swell equally. The density profile of thehydrogel films in the direction normal to the substrate is confrontedwith in-plane topography of the free surface. It results that thefree interface width is much larger than the roughness of the hydrogelfilm, suggesting pendant chains at the free surface. [ABSTRACT FROM AUTHOR]