Amorphous phase behavior and crystalline morphology in blends of poly(vinyl methyl ether) with isomeric polyesters: poly(hexamethylene adipate) and poly(ɛ-caprolactone)

Abstract

Two isomeric polyesters, poly(1,6-hexamethylene adipate) (PHA) and poly(ɛ-caprolactone) (PCL), were each blended with amorphous poly(vinyl methyl ether) (PVME) and investigated and compared in the crystalline and amorphous phases. The amorphous phase, Tg, and crystalline morphology of the PVME/PHA blend were compared with those of classical PVME/PCL. Both blend systems exhibit a similar peculiar asymmetry with positive deviation in Tg-composition relationships, and both are similarly miscible, with the PVME/PHA blend exhibiting χ12=−0.21; for PVME/PCL, χ12=−0.20. These values indicate that both blends are similarly miscible but have only quite weak interactions in the amorphous phase. Neat PHA shows a regime-I to -II transition, but neat PCL exhibits a regime-II to -III transition. On blending with PVME (at 20 wt%), both PVME/PCL and PVME/PHA blends undergo changes in crystallization temperature (Tc). Dendritic spherulites in the high-Tc (46 °C or above)-crystallized PVME/PHA blend assume a straight-stalk pattern (chrysanthemum flower pestles or banana stems). In contrast to the similarities in amorphous-phase miscibility, the crystalline phases of these two blends differ significantly. When crystallized at high Tc (46 °C or above), the PVME/PCL (20/80) blend assumes a fluffy feather-like dendritic pattern, which is dramatically different from the straight-stalk dendrites in the PVME/PHA (20/80) blend. The amorphous phase and crystalline morphology of the poly(vinyl methyl ether) (PVME)/poly(1,6-hexamethylene adipate) (PHA) blend were compared with those of the classical PVME/poly(ɛ-caprolactone) (PCL) system, isomeric to the former. Both blend systems’ amorphous phases are similarly miscible with χ12=−0.2. In contrast, the crystalline phases of these two blends differ significantly. When crystallized at high Tc (46 °C or above), the PVME/PCL (20/80) blend assumes fluffy feather-like dendrites (Graph-a), which are dramatically different from straight-stalk dendrites in the PVME/PHA (20/80) blend (Graph-b).