Chemical shrinkage and diffusion-controlled reaction of an epoxy molding compound

A methodology for the study of cure kinetics of a highly filled epoxy molding compound is presented. An equation relating the glass transition temperature-conversion relationship was first established. The degree of conversion can then be estimated when the calorimetric method is inadequate in measuring the heat of reaction in the diffusion-controlled regime. The cure reaction is modeled as a reaction of shifting order: it first reacts autocatalytically and later switches into diffusion control. The reaction in the diffusion-controlled regime is very slow and is modeled by an nth order kinetic equation. Both the linear coefficients of thermal expansion above and below the glass transition temperature decrease linearly with degree of conversion. Based on this linear coefficient of thermal expansion-conversion relationship, it is found that chemical shrinkage is an important factor that causes interfacial stresses when the epoxy molding compound adheres to a substrate of different materials.