Dynamics in miscible blends of polyisoprene and poly(p-tert-butyl styrene): thermo–rheological behavior of components

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For miscible blends of moderately entangled cis-polyisoprene (PI) and poly(p-tert-butyl styrene) (PtBS), viscoelastic and dielectric properties were examined over a wide range of temperature (T) to discuss the thermo–rheological behavior of respective components. Because PI has the type-A dipole, whereas PtBS does not, the slow dielectric response of the blends was exclusively attributed to the global motion of the PI chains therein. In most of the blends examined, the viscoelastic relaxation was much slower than the dielectric relaxation, and PI and PtBS behaved as the fast and much slower components, respectively. In those blends, the PI relaxation was thermo–rheologically complex because the slow PtBS chains quenched the dynamic frictional heterogeneity in the time scale of the PI relaxation. In contrast, the viscoelastic response of PtBS was thermo–rheologically simple because the fast PI chains smeared the heterogeneity for PtBS. Nevertheless, PtBS showed no ordinary relaxation associated with the entanglement plateau but did exhibit Rouse-like relaxation slower than the entanglement-free Rouse process. This slow Rouse-like relaxation was attributed to the pseudo-constraint release mechanism for the PtBS chains activated by the global motion of the PI chains. A simple model based on this molecular picture described the G* data of the blends well.
2012-01-15