MISCIBLE BLENDS OF 2 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 fluori de) (PVF2) and poly(1,4-butylene adipate) (PBA), both semicrystalline polymers, have been investigated using differential scanning calorimet ry and light-scattering techniques. The phase diagram of this blend sy stem exhibits a single glass transition temperature over the entire co mposition range, two distinct melting transitions, and a cloud-point c urve above a lower critical solution temperature of 235 degrees C. A d epression of the equilibrium melting point of both PVF2 and PEA is obs erved. From the melting point data of the high-T-m, component, PVF2, a value for the polymer-polymer interaction parameter of (chi 12) = -0. 19 was derived using the Flory-Huggins equation. This implies that PVF 2/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 PVF 2 is semicrystalline at temperatures of PEA melting. Infrared spectros copy measurements focusing on the carbonyl absorption band of PEA reve al. a slight shift in peak position toward lower frequencies due to bl ending, indicating that the thermodynamic miscibility of the PVF2/PBA pair arises from weak. specific interactions involving the polyester c arbonyl group. In spite of their miscibility, blends of PVF2 and PBA e xhibit a complex phase behavior and may form multiphase systems. Of pa rticular interest is the three-phase morphology in which two distinct crystalline phases (PEA and PVF2) coexist with an intimately mixed amo rphous phase. This morphology is observed at room temperature over a v ery broad composition range.