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 bisphenol-A based epoxy resin and internally epoxidized polybutadiene rubber have been studied as a function of initial rubber content, stoichiometry and cure cycle of the epoxy resin. It is shown that both the glass transition temperature of the epoxy-rich continuous phase, T(gE(r)), and the apparent enthalpy of activation associated with this transition, DELTAH(aE(r)), are sensitive to the state of the rubber in the sample. Specifically, dynamic mechanical analysis can be used to distinguish between rubber dissolved in the matrix (plasticizer), incorporated into the network (flexibilizer) or phase separated (toughener). Furthermore, it is demonstrated that the Gordon-Taylor equation rather than the more commonly used Fox equation should be used to model the effect of dissolved rubber on T(gE(r)) and that the Gordon-Taylor equation can also be extended to describe the variations of DELTAH(aE(r)). Ultimately this equation can be generalized to predict the glass transition temperature of a sample containing both dissolved and phase separated rubber.