Double-stage phase separation in dynamically asymmetric ternary polymer blends

Abstract

In this work, the phase separation behavior of ternary blends of polystyrene/poly(vinyl methyl ether)/polyisoprene, PS/PVME/PI, and polystyrene/poly(vinyl methyl ether)/poly(ethyl methacrylate), PS/PVME/PEMA are investigated. Ternary blends of PS/PVME/PI and PS/PVME/PEMA are expected to exhibit complex phase separation behavior since PS and PVME have a lower critical solution temperature (LCST) with viscoelastic phase separation (VPS) behavior, while PI/PS, PI/PVME, PEMA/PS, and PEMA/PVME have an upper critical solution temperature (UCST) behavior. 2D and 3D phase diagrams for these two ternary systems are obtained by a compressible regular solution model. Casting the solutions of PS/PVME/PI and PS/PVME/PEMA blends forms two phase-separated domains in most compositions: (1) PI-rich or PEMA rich, and (2) PS/PVME-rich. Post-annealing of such samples at 110 °C leads to a second-stage phase separation due to unfavorable interaction of PS and PVME. Such behavior, which is observed for the first time, provides a new potential method for making different morphologies with the same system by changing annealing parameters and composition. The kinetics and morphology of ternary blends during phase separation are studied by optical microscopy and scanning electron microscopy.