Flow-induced demixing of polyisoprene/poly(4-tert butyl styrene) with high dynamic contrast

This study places a focus on flow-induced demixing of polyisoprene (PI) and poly(4-tert butyl styrene) (PtBS) polymer blends with high dynamic contrast. The rheological response is governed by the more immobilized PtBS chains. In contrast, the dielectric response at low frequency reflects exclusively the normal mode of PI chains having type-A dipole parallel along the chain backbone. These features enable selective detection of the component dynamics of PtBS or PI chains under either the small amplitude oscillatory shear or the nonlinear steady shear through a combination of rheological and dielectric techniques. We find the Cox–Merz rule fails significantly for the PtBS/PI blends, which is attributed to flow-induced demixing when the shear rate is higher than the relaxation rate of PtBS chains and lower than that of PI chains. The flow-induced demixing is further supported by varying the molecular parameters of PtBS, copolymerizing PtBS with polystyrene, as well as by the rheo-dielectric measurements that show a broadening of the PI relaxation mode distribution. This demixing could be partly driven by the increased conformational entropy of the PI chains after segregation from the surrounding restrictive PtBS chains. Graphical abstract