SEGMENTAL RELAXATION AND THE CORRELATION OF TIME AND TEMPERATURE DEPENDENCIES IN POLY(VINYL METHYL-ETHER) POLYSTYRENE MIXTURES

An analysis is presented of the glass transition dispersion in the dielectric spectrum of poly-(vinyl methyl ether) (PVME) mixed with polystyrene (PS). The spectrum is dominated by the response of the PVME, enabling its molecular motions to be studied as a function of both local composition and temperature. It is shown that through their effect on the degree of intermolecular cooperativity of the segmental dynamics concentration fluctuations effect a marked asymmetry in the band shape. PVME chain units in a PS-rich environment contribute to the dielectric loss primarily at lower frequencies and are characterized by more cooperative segmental relaxation. The dielectric response of these segments is more sensitive to temperature than PVME segments relaxing in a PVME-rich environment. This results in a failure of time-temperature superpositioning. The correlation observed for the time and temperature dependencies of PVME relaxation near its glass transition temperature is a consequence of intersegmental cooperativity.