Miscible blends prepared from two crystalline polymers

Differential scanning calorimetry was used to determine the miscibility behavior of several polyester/Saran blends, the two polymers forming these blends being semicrystalline. It was found that Saran is miscible with polycaprolactone (PCL), polyvalerolactone, poly(butylene adipate), and poly(hexamethylene sebacate) since a single glass transition temperature Tg was observed at each composition. However, immiscibility was found between Saran and poly(ethylene adipate), poly‐(ethylene succinate), poly(β‐propiolactone), and poly(α‐methyl‐α‐n‐propyl‐β‐propiolactone) since two Tg's were recorded at several compositions. Blends were then obtained containing, over a wide range of composition, a miscible amorphous phase and two different types of crystals. From melting‐point depression data on PCL and Saran crystals, thermodynamic interaction parameters χ were calculated and found to be different for PCL‐rich blends and for Saran‐rich blends. This result suggests a variation of χ with composition. Saran is a polymer which does not contain α‐hydrogens and its miscibility with polyesters may result from a β‐hydrogen bonding interaction or a CO/CCl dipole‐dipole interaction.