PHASE-SEPARATION STUDIES OF HEAT-CURED ATU-FLEXIBILIZED EPOXIES

Chemical incorporation of a flexible molecule into a heat-cured epoxy offers an important route by which to toughen the epoxy and tailor its ultimate material properties. Acrylate-terminated urethane (ATU) flex ibilizers containing polypropylene glycol have been employed in the pr esent work to modify epoxies composed of a diglycidyl ether of bisphen ol-A and bis(4-aminocyclohexyl) methane. Differential scanning calorim etry, dynamic mechanical analysis and electron microscopy reveal that the flexibilizer and epoxy undergo phase separation during cure when t he flexibilizer loading or molecular weight is sufficiently high. Part ial phase miscibility, deduced from both glass transition temperature shifts and stress-relaxation behaviour, is interpreted here in light o f thermodynamic and free-volume considerations.