COMPOSITION OF THE CONTINUOUS-PHASE IN PARTIALLY MISCIBLE BLENDS OF EPOXY-RESIN AND EPOXIDIZED RUBBER BY DYNAMIC-MECHANICAL ANALYSIS

The dynamic mechanical properties of blends of diglycidyl ether of bis phenol-A based epoxy resin and internally epoxidized polybutadiene rub ber have been studied as a function of initial rubber content, stoichi ometry and cure cycle of the epoxy resin. It is shown that both the gl ass transition temperature of the epoxy-rich continuous phase, T(gE(r) ), and the apparent enthalpy of activation associated with this transi tion, DELTAH(aE(r)), are sensitive to the state of the rubber in the s ample. Specifically, dynamic mechanical analysis can be used to distin guish between rubber dissolved in the matrix (plasticizer), incorporat ed into the network (flexibilizer) or phase separated (toughener). Fur thermore, it is demonstrated that the Gordon-Taylor equation rather th an the more commonly used Fox equation should be used to model the eff ect of dissolved rubber on T(gE(r)) and that the Gordon-Taylor equatio n can also be extended to describe the variations of DELTAH(aE(r)). Ul timately this equation can be generalized to predict the glass transit ion temperature of a sample containing both dissolved and phase separa ted rubber.