Structure and Dynamics of Melts of Multiarm Polymer Stars

We probe the structure−dynamics relationship in melts of star polymers with high functionality using small-angle X-ray scattering, rheology, and Monte Carlo computer simulations. These materials represent model steric soft spheres, which order in a liquidlike structure on a macromolecular scale because of the impenetrability of the cores. This is a consequence of the complex star topology, which is characterized by an inhomogeneous intrastar monomer density distribution. The signature of the structure appeares in the dynamics of these systems as a slow terminal relaxation process, in addition to the classical faster arm retraction mechanism. The slow process is attributed to the structural rearrangements of the stars within their liquidlike order and can be thought of as a reflection of their colloidal nature. We identify the dependence of this dynamic mode on the molecular parameters, i.e., star functionality and arm size.