Morphology profiles generated by temperature gradient in PMMA modified epoxy system

A diglycidyl ether of bisphenol-A (DGEBA) epoxy resin was modified with 15 wt% of poly(methylmethacrylate) (PMMA) and cured with a stoichiometric amou nt of 4,4'-diamino diphenyl methane (DDM). The reactive mixture was cured i n a heated mold with different gradients of temperature. Temperature profil es in the mold were imposed by generation of a heat. flux from the base, su pported on a hot plate, and the top, cooled with water; they were measured along the mold. Depending on the thermal history in each position of the mo ld, the competition between the phase-separation process and reaction kinet ics produces opaque or transparent zones. Phase separation can also occur i n the postcure process while the gelation does not take place before. There fore, a thermoset plate with gradient of morphology and properties was obta ined. Mass fractions of PMMA dissolved in the matrix were calculated with t he Fox equation from glass transition temperatures measured along the mold. They were related to morphologies developed during curing. The superpositi on of the phase diagrams with the conversion-temperature trajectories durin g cure permitted an explanation of the morphology gradients generated.