Dynamics of each component in miscible blends of polyisoprene and polyvinylethylene

The dynamics of the individual components in 1,4-polyisoprene/polyvinylethylene (PIP/PVE) miscible blends are studied using dynamic stress-optical measurements. While the homopolymers are thermorheologically simple and obey the stress-optic rule, the blends show failure of time-temperature superposition and complex stress-optic behavior. The way in which the stress-optic rule fails reveals the relaxation dynamics of each species. The dynamic modulus and complex birefringence coefficient are analyzed to infer the relaxation of each component. The entanglement molecular weight, M_e, and monomeric friction coefficient, ₀, of each species as a function of blend composition and temperature are determined from the contribution of each species to the dynamic modulus. The effect of blending on M_e of each component is small; however, its effect on ₀ of each species is dramatic. Blending strongly speeds the rate of relaxation of the high T_g component (PVE), while more modestly slowing the relaxation of the low T_g component (PIP). The dynamics of each species have different temperature dependencies in the blend, which leads to the failure of the superposition principle. Furthermore, both the difference between the friction coefficients of the two species and the difference in their temperature dependencies is greater in blends rich in the high T_g material (PVE).