Influence of the molecular weight of a modifier on the phase separation in an epoxy thermoset modified with a thermoplastic

Abstract The effect of varying the molecular weight of a thermoplastic modifier on the phase separation in polystyrene (PS)-modified epoxy/amine blends was investigated by comparing blends with PS of different molecular weights. A thermodynamic analysis of polymerization-induced phase separation was performed using a model based on the Flory–Huggins theory, from which the phase diagram and species distribution in the separated phases were calculated. Morphologies developed by the blends were studied in terms of concentration and molecular weight of modifier. Trends in morphologies and thermodynamics of phase separation were exposed and discussed. An increase in the molecular weight of modifier caused a decrease in the miscibility of blend affecting phase diagram, molecular fractionation between the separated phases and morphologies developed showing that molecular weight is a tool to control the final materials.