Dynamical heterogeneity in the thermodynamically miscible polymer blend of poly(vinyl ethyl ether) and styrene-co-p-hydroxystyrene copolymer

The dynamic heterogeneity of the thermodynamically miscible blend of poly(vinyl ethyl ether) and styrene-co-p-hydroxystyrene (PVEE/SHS) has been investigated using broadband dielectric spectroscopy (DRS) and other experimental probes. In our previous study of PVEE/poly(p-hydroxystyrene) blends, we found that the segmental relaxations of the component polymers can be coupled if there is sufficient intermolecular hydrogen bonding. For SHS/PVEE blends, however, two segmental relaxations are observed in the DRS spectra, even for blends with a fraction of intermolecular hydrogen bonds as large as that in the PVPh/PVEE blend, in which a single segmental relaxation was found as a result of the coupling effect from the hydrogen bonds. This behavior is explained by the existence of unfavorable interactions between PVEE and the styrene units in SHS, which is supported by the immiscibility between PS and PVEE. The repulsive force endows the non-hydrogen-bonded PVEE segments with more freedom to relax, so that they can be distinguished from the relaxation of intermolecularly hydrogen-bonded PVEE-SHS segments. This indicates more significant dynamic heterogeneity in SHS/PVEE than in PVEE/poly(p-hydroxystyrene) blends.