OBSERVATION OF THE COMPONENT DYNAMICS IN A MISCIBLE POLYMER BLEND BY DIELECTRIC AND MECHANICAL SPECTROSCOPIES

Dielectric and mechanical relaxation measurements of the local segmental relaxation in miscible blends of poly(vinylethylene) (PVE) and polyisoprene (PIP) have been made under isothermal conditions over a wide range of frequency. Taking advantage of the prominence of respectively the PVE contribution to dielectric relaxation and the PIP contribution to mechanical relaxation, we are able to resolve the dynamics of each component in some of the blends. From the observed dynamics of individual components, we establish as experimental facts that the most probable local segmental relaxation time of each component has a different magnitude as well as different temperature dependence. Moreover, the relaxation spectrum of each component broadens as temperature is decreased. Thus a breakdown of thermorheological simplicity occurs not only in the dynamics of each component but a fortiori when the contributions from both components are considered together. The degree to which these effects manifest themselves depends on the blend composition. All these experimental features are shown to be in accord with a theory of segmental dynamics for blends that is obtained as a generalization of the coupling model for homopolymers by taking into account local concentration fluctuations.