Ternary Miscibility in Blends of Three Polymers With Balanced Binary Interactions

This study demonstrates and discusses ternary miscibility in a three-polymer blend system based on balanced binary interactions. A truly miscible ternary blend comprising poly(ε-caprolactone) (PCL), poly(benzyl methacrylate) (PBzMA), and poly(vinyl methyl ether) (PVME), was discovered and reported. Miscibility with phase homogeneity (excluding the PCL crystalline domain) in a wide composition range has been demonstrated using criteria of thermal transition behavior, cloud point, and microscopy characterization. At ambient temperature, the three-polymer ternary system is completely miscible within the entire composition range (i.e., no immiscibility loop). However, at slightly elevated temperatures above the ambient, phase separation readily occurred in this originally miscible ternary blend. A quite low "lower critical solution temperature" (LCST) near 75°C was found for the ternary blend, which is much lower than any of those for the binary pairs. Balanced interactions with no offsetting Δχ among the three binary pairs were a key factor leading to a ternary miscible system.