Miscible blends of two crystalline polymers .3. Liquid-liquid phase separation in blends of poly(vinylidene fluoride) poly(butylene adipate)

Phase behavior and dynamics of liquid-liquid phase separation in binary blends of crystalline polymers, viz., poly(vinylidene fluoride) (PVF2) and poly(butylene adipate) (PBA), have been studied by means of time-resolved lightscattering. According to our previous calorimetric study, a single glass transition and two distinct melting endotherms were discerned over the entire composition range. The systematic movement of the glass transition with composition and the lowering of the melting point of the PVF2 crystals indicate trends of a typical miscible blend. However, the dual melting peaks suggest that cocrystallization does not occur. In the melt state (similar to 60 deg above the melting temperature of the PVF2 crystals), a thermally reversible lower critical solution temperature (LCST) was observed. Several temperature jump experiments were undertaken in a light-scattering apparatus at a 50/50 PVF2/PBA composition from a single-phase melt state (200 degrees C) to a two-phase region (238, 240, 245, and 250 degrees C). A similar experiment was performed from a crystalline solid state (ambient temperature) to 238 and 240 degrees C for the elucidation of the effect of crystal melting on the kinetics of phase separation. Time evolution of structure factors (scattering intensity profiles) has been analyzed in the context of nonlinear and scali scaling theories of spinodal decomposition.