Effects of Chain Topology on the Tracer Diffusion in Star Polyisoprenes

Fluorescence correlation spectroscopy (FCS) was employed to study the effect of chain topology on the small tracer diffusion in linear and star-shaped 1,4-polyisoprenes (PIS) at temperatures well above the glass transition. In the linear polyisoprene, a Fickian diffusion behavior was observed that is characterized by it single diffusion coefficient. In contrast, the diffusion of the same tracers in three-arm star PI wits non-Fickian and could best be described assuming two diffusion modes. The fast mode diffusion has the same magnitude and temperature dependence as the tracer diffusion in linear PI. The slow mode present only in the star polymer is apparently related to topological restrictions that cause retention of the tracer. The temperature dependence of the retention time is very similar to that of the polymer arm relaxation, indicating a direct correlation between the two dynamic processes.