Melt Dynamics in Complex Polymer Systems: Star-shaped Polymers and Polymer Nanocomposite Films

Abstract

The study of dynamic relaxations in polymer chains has been one of the cornerstones of polymer physics research for over half a century. Increased understanding of polymer chain relaxations has led to the development of macromolecules for packaging, drug delivery and sensor applications. As the challenges for these applications have become more demanding, it is now necessary to tailor polymer relaxation properties in more detailed and specific ways. In this thesis, we investigated two methods for tailoring polymer chain dynamics: (1) manipulation of molecular architecture and (2) introduction of inorganic nanoparticles into a polymer host. First, we demonstrate that the translational dynamics in star-shaped polystyrene can be tailored to behave as either a linear polymer or a soft colloid through the control of the star-shaped polymer molecular parameters such as functionality and arm molecular weight. We show that this is due to entropic intermolecular interactions caused by a tunable high-density core region close to the star branch point. Second, we show that in thin polymer films, the translational dynamics of the host polymer can be tailored through the introduction of inorganic polymer chain-end grafted particles. When these particles are well-dispersed throughout the polymer host, the relaxations of the host are shown to be strongly dependent on the confinement of the nanoparticles and the suppression of nanoparticle dynamics – leading to an order of magnitude increase in viscosity. If the particles are not well-dispersed, they are shown to segregate to the film interfaces and cause a region of high viscosity at the film free surface. This work highlights influences of molecular architecture, confinement and interfacial interactions on the dynamic relaxations of polymers and illustrates how these influences can be used to tailor polymer properties.