Crystallization-Induced Confinement Enhances Glassy Dynamics in Star-Shaped Polyhedral Oligomeric Polysilesquioxane–Isotactic Polystyrene (POSS–iPS) Hybrid Material

In semicrystalline polymers, the segments around the crystallites typically relax significantly slower than in the purely amorphous phase. This results in an, on average, slower dynamics. Here we present a contrary effect in a star-shaped polymer based on a polyhedral oligomeric silesquioxane (POSS) molecule as center and isotactic polystyrene arms. Measurements by means of broadband dielectric spectroscopy reveal a reduction of the mean relaxation time by up to 1 decade. Analyzing the relaxation time distribution unravels three moieties of different dynamics beyond the crystalline fraction. These are assumed to form respective domains: a rigid amorphous fraction around crystallites, a mobile amorphous fraction, and a confined amorphous fraction of enhanced dynamics presumably located around the POSS centers. Probably, the crystallites in combination with the starlike architecture stabilize the average volume which balances the higher density of the growing crystallites by an increase in free volume in the amorphous domains