Dynamics of a poly(isoprene)/poly(vinyl ethylene) blend revisited: Component polymer relaxation and blend behavior

Motivated by recent molecular dynamics simulation studies of miscible blends of dynamically disparate polymers, we have revisited the experimentally measured dielectric relaxation in a 50/50 blend of poly(isoprene) and poly(vinyl ethylene) (PI/PVE). In contrast to efforts to explain the dielectric loss in PI/PVE blends in terms of a distribution of local environments leading to a broad distribution of segmental relaxation times (the so-called concentration fluctuation model), our analysis indicates that there is no evidence for significant broadening of the relaxation processes in the component polymers upon blending. Rather, we find that the dielectric loss of the 50/50 PI/PVE blend can be represented as a sum of α- and β-relaxation processes for the component polymers represented with Havriliak–Negami functions whose shape and relaxation strength are consistent with those obtained for the pure PI and PVE melts. The α-relaxation process for the PVE component was found to be dramatically influenced by blending, moving to much higher frequency with moderate narrowing, while the α-relaxation process for the PI component shifted to somewhat lower frequency with slight broadening, consistent with our MD simulations of a model blend and 2D NMR measurements on PI/PVE blends. In contrast, the β-processes in the PVE and PI components were found to be essentially uninfluenced by blending, with the latter accounting for the significant high-frequency loss observed in the PI/PVE blend.