Polymer topology and diffusion: a comparison of diffusion in linear and cyclic macromolecules

Diffusion experiments using polystyrene (PS) molecules of three different topologies, linear, ring, and microgel, were performed. Tracer diffusion of linear PS in ring matrices was found to be nearly identical to that in linear matrices, a surprising result in view of current theories for matrix-dependent tracer diffusion. The first unambiguous data showing a lower limit for the tracer diffusion coefficient D* of ring molecules in linear PS of high molecular weight are presented. These data support the hypothesis that ring-shaped molecules can undergo a form of reptation. The tracer diffusion coefficient of ring molecules of molecular weight M in intramolecularly cross-linked PS (microgel) matrices was found to scale as M-4.5+/-0.2, a higher M dependence than has been observed for rings diffusing in linear matrices.