Phase separation process in poly(epsilon-caprolactone)-epoxy blends

Abstract

Phase separation process in poly(epsilon-caprolactone)-epoxy blends (PCL-epoxy) cured by 4,4'-diaminodiphenyl sulfone (DDS) was investigated by OM and SEM. The blend compositions higher than the critical point exhibit macrophase separation by the spinodal decomposition (SD) mechanism of the epoxy and results in the epoxy particles being dispersed in the matrix. These epoxy particles grow larger gradually and connect to each other to give macrophase epoxy domains with irregular shape. After that, two more stages of microphase separations bake place via a nucleation and growth (NG) mechanism and result in smaller epoxy particles being dispersed in the matrix. Blend compositions lower than the critical point exhibit the SD or NG mechanisms of PCL, but the microphase separation is observed only within the epoxy matrix. These phase separation mechanisms can be illustrated successfully by the phase diagram constructed by the spinodal and binodal curves. Hydrogen bonding between protons from the epoxy with carbonyls from PCL has been investigated by FTIR. The mixing free energy reduction by the hydrogen bonding can contribute to the LCST behavior rather than the UCST behavior predicted by the Flory-Huggins equation based on only nonpolar interactions.