Polystyrene with different topologies: Study of the glass transition temperature in confined geometry of thin films

The glass transition behaviour of polystyrene (PS) with systematically varied topologies (linear, star-like and hyperbranched) confined in nanoscalic films was studied by means of spectroscopic vis-ellipsometry. All applied PS samples showed no or only a marginal depression in glass transition temperature Tg in the order hyperbranched PS (5 K) > star-like PS (3 K) > linear PS (0 K) for the thinnest films analyzed. The Tg behaviour was accompanied by the observation of the film density in dependence of film thickness. A maximum decreased density of about 7% for hyperbranched PS and 5% for star-like PS and again no deviation in density of bulk was found for linear PS. Accordingly, we deduce from these results considering an experimental accuracy of about ± 2 K for Tg and up to ±3% for film density, that the polymer topology only barely influences Tg in the confinement of thin films.