PHASE-BEHAVIOR OF POLYLACTIDES IN SOLVENT-NONSOLVENT MIXTURES

Isothermal phase diagrams for the semicrystalline poly-L-lactide (PLLA ) and the amorphous poly-DL-lactide (PDLLA) in combination with severa l solvent-nonsolvent combinations (dioxane/water, dioxane/methanol, ch loroform/methanol, and NMP/water) have been determined. The locations of the liquid-liquid miscibility gap, the solid-liquid miscibility gap and the vitrification boundary in the isothermal phase diagrams at 25 degrees C were identified. The liquid-liquid miscibility gap for the systems with PLLA was located in the same composition range as the cor responding systems with PDLLA. For the systems containing PLLA solid-l iquid demixing was thermodynamically preferred over liquid-liquid demi xing. Attempts were made to correlate the experimental findings with p redictions on the basis of the Flory-Huggins theory for ternary soluti ons using interaction parameters derived from independent experiments. Qualitative agreement was found between the theoretical predictions a nd the experimentally obtained liquid-liquid miscibility gap. No good agreement was found for the solid-liquid miscibility gap. (C) 1996 Joh n Wiley & Sons, Inc.