Miscible Blends of Two Crystalline Polymers. 1. Phase Behavior and Miscibility in Blends of Poly(vinylidene fluoride) and Poly(1,4-butylene adipate)

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-Tm 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-Tm 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. Inf...