Peculiarities of the segmental dynamics in amorphous miscible polymer blends as a consequence of the common nature of α and β relaxations

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Abstract
Amorphous polystyrene-poly(α-methyl styrene) (PS/PMS) and polysty-rene-poly(vinyl methyl ether) (PS/PVME) miscible blends have been studied in detail by differential scanning calorimetry. A number of segmental dynamics characteristics, including the temperature dependence of motional activation energies over the range from the β relaxation region to the glass transition, the scale of motional unit events, and the degree of intermolecular cooperativity for segmental motion, have been determined. A number of peculiarities of Tg manifestation as well as two types of segmental dynamics heterogeneity in the glass transition have been observed. They could be explained and predicted quantitatively, proceeding from the concept of the common segmental nature of the α and β relaxations in flexible chain polymers, as a consequence of a partial or complete breakdown of intermolecular cooperation (“individualizing”) or segmental motions. A linear correlation between the segmental dynamics activation energy and degree of intermolecular cooperativity has been found.