An investigation was conducted to determine how the advancement of chemical reactions and the prepolymer molecular weight affect the reorientational dynamics and intermolecular cooperativity in model epoxy-amine systems. Experimental results were obtained by dielectric spectroscopy over a wide range of frequency and temperature. A strong effect of the progress of reaction on reorientational dynamics was noted and an explanation was put forward within the framework of the coupling theory, marking the first time this concept was applied to reactive systems. It was proposed that the molecular-level characteristics that govern the intermolecular cooperativity of reactive systems can be classified into two categories : (1) molecular architecture, determined by molecular symmetry, rigidity, and steric hindrance, and (2) dielectric architecture, determined by the type and concentration of all dielectrically active species. Both molecular and dielectric architecture Vary in the course of chemical reaction, and the overall direction in which the cooperativity shifts is governed by the interplay between these two phenomena.