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

• Thermodynamics and morphology of PIPS in a modified epoxy system were studied.
• The effect of the modifier molar mass on the phase separation was investigated.
• A thermodynamic model taking polydispersities of components into account was used.
• The fractionation of the components in the emergent phase was predicted.
• Morphological trends depending on amount and molar mass modifier were studied.

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.

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