Effect of temperature and pressure on the dynamic miscibility of hydrogen-bonded polymer blends

The dynamic miscibility of poly(4-vinylphenol)/poly(vinyl ethyl ether) (PVPh/PVEE) blends, with a T _g contrast of 186 K, as well as the PVEE segmental dynamics have been investigated by temperature- and pressure-dependent dielectric spectroscopy. In PVEE the pressure coefficient of T _g amounts to 0.215 K/MPa, and its apparent activation volume displays the usual T dependence. Although both temperature and volume contribute to the segmental dynamics, the former has a stronger influence within the T and P investigated. In the blends, dynamic heterogeneity is suppressed because of hydrogen bonds that couple the components' segmental dynamics. In the PVEE-rich blends, increasing temperature and pressure results in the broadening of the distribution of relaxation times through the weakening of hydrogen bonds and the associated decoupling of the segmental dynamics. A central result of the present study is the identification of a critical temperature above which the system becomes increasingly heterogeneous.