Variations of the polymer dynamic of different systematically varied polyester architectures in the confinement of thin films were studied by temperature dependent spectroscopic vis-ellipsometry. The architectures were tailored in order to evaluate (a) the impact of different polymer backbones (hyperbranched, branched or linear and aromatic, aromatic-aliphatic or aliphatic), (b) the influence of functional groups (hydroxyl, benzoyl, tert-butyldimethylsilyl) and (c) the role of interfacial interactions (attractive, repulsive) with the silicon substrate. Possible reasons for the deviation of the glass transition temperature T-g in thin polymer films (10-800 nm) from the bulk value are described and compared to the literature. It was found that the functional groups of the applied polymers have the largest effect on T-g. Beside interfacial interactions, chemical and physical reactions in the polymer film are playing a significant role. (C) 2009 Elsevier Ltd. All rights reserved.