The phase behavior and miscibility of blends of
poly(vinylidene fluoride) (PVF2) and
poly(1,4-butylene adipate) (PBA), both semicrystalline polymers, have been
investigated using differential
scanning calorimetry and light-scattering techniques. The phase
diagram of this blend system exhibits
a single glass transition temperature over the entire composition
range, two distinct melting transitions,
and a cloud-point curve above a lower critical solution temperature of
235 °C. A depression of the
equilibrium melting point of both PVF2 and PBA is observed.
From the melting point data of the high-T
m component, PVF2, a value for the
polymer−polymer interaction parameter of χ12 =
−0.19 was derived
using the Flory−Huggins equation. This implies that
PVF2/PBA blends are thermodynamically miscible
in the melt. The extent of the melting point depression for the
low-T
m component, PBA, is much
smaller
than it is for PVF2, which is attributed to the fact that
PVF2 is semicrystalline at temperatures of PBA
melting. Infrared spectroscopy measurements focusing on the
carbonyl absorption band of PBA reveal
a slight shift in peak position toward lower frequencies due to
blending, indicating that the thermodynamic
miscibility of the PVF2/PBA pair arises from weak specific
interactions involving the polyester carbonyl
group. In spite of their miscibility, blends of PVF2
and PBA exhibit a complex phase behavior and may
form multiphase systems. Of particular interest is the three-phase
morphology in which two distinct
crystalline phases (PBA and PVF2) coexist with an
intimately mixed amorphous phase. This morphology
is observed at room temperature over a very broad composition
range.