Dynamics of Hyperbranched Polymers under Confinement: A Dielectric Relaxation Study

The effect of severe confinement on the dynamics of three different generations of hyperbranched polyesters of the Boltorn family is investigated by dielectric relaxation spectroscopy (DRS). The polymer chains are intercalated within the galleries of natural montmorillonite (Na+-MMT), thus forming 1 nm polymer films confined between solid walls. The structure of the nanocomposites is studied with X-ray diffraction and the thermal behavior of the polymers in bulk and under confinement is determined by differential scanning calorimetry. The glass transition temperatures of the polymers show a clear dependence on the generation whereas the transition is completely suppressed when all the polymer chains are intercalated. The dynamic investigation of the bulk polymers reveals two sub-Tg processes, with similar behavior for the three polymers with the segmental relaxation observed above the Tg of each polymer. For the nanocomposites, where all the polymer chains are severely confined, the dynamics show significant differences compared to that of the bulk polymers. The sub-Tg processes are similar for the three generations but significantly faster and with weaker temperature dependence than those in the bulk. The segmental process appears at temperatures below the bulk polymer Tg, it exhibits an Arrhenius temperature dependence and shows differences for the three generations. A slow process that appears at higher temperatures is due to interfacial polarization.