Segmental relaxations in the neat components and the blend of poly(4-vinylphenol) (PVPh) with poly(ethylene-co-vinyl acetate) (EVA, with 70 wt % vinyl acetate) are studied by broadband dielectric spectroscopy at different temperatures and hydrostatic pressures (up to 750 MPa). Pressure retards the relaxation, with a consequent increase of the glass transition temperature (T g). The pressure coefficient of Tg is 158 C/GPa for the neat EVA, with temperature and pressure found to exert a comparable effect on segmental relaxation. The shape of the EVA segmental relaxation function, however, is the same for different temperature-pressure conditions at a given relaxation time. On the other hand, PVT measurements on PVPh indicate that temperature is more important than pressure in determining the segmental relaxation time, due to the presence of strong hydrogen bonding. For blends with 20% and 30% PVPh, similar pressure-dependent increases of Tg are observed, although contributions from T and P to segmental relaxation are again comparable, despite the hydrogen bonding between PVPh and EVA. Although both high pressure and temperature reduce the concentration of hydrogen bonds in the blends, which tends to decouple the components' segmental relaxation processes, the relaxation time distribution in the blends is narrowed with increasing pressure at a given relaxation time. This behavior is interpreted by considering the additional mobility achieved from breaking hydrogen bonds at high pressures and high temperatures for the hydrogen-bonded (and thus slow) PVPh-EVA segments compared with the fast relaxation of unassociated EVA segments.

Dynamical homogeneity was observed in mixtures of PVME with two small moleculess4ethylphenol [EPh] and bis(4-hydroxyphenyl)methane [BPM]sby broadband dielectric spectroscopy. TTS is valid in mixtures with EPh concentrations up to 50% and for BPM content from 2 to 30%, and all have the same segmental relaxation time distribution as neat PVME. This behavior is attributed to the strong intermolecular hydrogen bonding, increased mixing entropy, relatively small Tg contrast, the absence of self-concentration effects, and reduced interchain cooperativity. However, PVME/toluene mixtures exhibit a slightly broader segmental relaxation distribution due to the absence of hydrogen bonding. We also found that strong intermolecular associations are capable of slowing down the secondary relaxation of PVME. Spatial heterogeneity is expected in mixtures with very low BPM contents based on the effect of stoichiometry, and two relaxing segments are possible in 2% BPM/PVME mixtures.

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.