DYNAMIC HETEROGENEITY IN A MISCIBLE POLYMER BLEND

Measurements of dynamic mechanical spectra in the glass transition region for miscible blends of 1,4-polyisoprene and poly(vinylethylene) are reported. In accordance with previous measurements of heat capacity and thermal expansivity, the transition zone is found to be extraordinarily broad when the blend has a high concentration of poly(vinylethylene). The application of the coupling model to the data suggests that this breadth is a manifestation of an inhomogeneous distribution of relaxation times and coupling parameters engendered by concentration fluctuations. Although not experimentally observable herein, a consequence of this dynamical heterogeneity is deviation from the principle of time-temperature superpositioning for miscible polymer mixtures in the glass transition region. The latter is consistent with solid-state C-13 NMR measurements reported previously.