Broadband dielectric spectroscopy (BDS), specific heat spectroscopy (HCS) and capacitive scanning dilatometry (CSD) are used to study the glass transition and segmental dynamics in thin supported polystyrene (PS) films. Different molecular weights (M-w = 50 kg/mol, M-w = 260 kg/mol, M-w = 1408 kg/mol) and annealing protocols are employed in the study. The segmental dynamics is independent of the film thickness for each M-w, in the temperature window of the dielectric measurement. The thermal glass transition temperature, T-g, measured by CSD depends on the film thickness and shows also a dependence on M-w. These observations are explained in terms of the formation of irreversibly adsorbed layer due to chain adsorption on the Al substrates during annealing. (C) 2013 Elsevier B.V. All rights reserved.