Enhanced Tg-Confinement Effect and Related Physical Aging Behavior in Crosslinked Polystyrene Characterized By Ellipsometry

The effects of nanoscale confinement on the glass transition temperature, Tg, and related physical aging behavior are studied in crosslinked polystyrene (PS). Crosslinked PS films are achieved by thermally annealing the spin-cast linear precursor (polystyrene-vinylbenzocyclobutene) films with varying thicknesses at 250 ^oC. Tg reductions are observed with ellipsometry measurements of both supported linear and crosslinked PS films, with confinement effects being enhanced in crosslinked polystyrene compared to the linear precursor. The greater magnitude of Tg reduction observed in confined crosslinked PS films can be rationalized by the increased bulk fragility induced by crosslinking. Physical aging rate in bulk crosslinked PS is characterized by continuously monitoring the decrease in film thickness with aging time, and is also compared with that in the direct linear precursor. It is observed that crosslinked bulk PS undergoes slower physical aging rate than its direct linear precursor between Tg and ~ Tg – 60 ^oC. Effects of confinement on fragility and physical aging in the crosslinked PS will also be discussed in this study.