Fragility and the Glass Transition of Geometrically Confined Polynorbornenes

Over the past twenty years many studies have shown a reduction in the glass transition temperature (Tg) of thin polymer films confined on the nanoscale when supported on non-attractive substrates or free-standing. These results have been explained by the propagation of enhanced mobility from the free-surface into the polymer film. Many questions remain as to the varying length scale over which Tg decreases, the magnitude of the Tg perturbation observed for different polymers as well as the role cooperatively rearranging regions play in Tg. In this study we measure the dynamic fragility, cooperative length scale, and confined Tg for a series of chemically similar polynorbornenes. We do not see a clear trend in bulk fragility, cooperative length scale, and the magnitude of the Tg perturbation over a wide range of fragilities. Utilizing the unique capabilities of flash differential scanning calorimetry we are also able to quantify the influence of confinement on the fragility and cooperative motion of polynorbornenes.