The formation of heterogeneous structure through intramolecular reaction is an important feature of the free radical cross-linking copolymerization of methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDMA). Such structure formation affects not only the curing behavior but also the rheological changes of the resin. In this study, the reaction kinetics, rheological changes, and the size distribution of formed polymers are measured by differential scanning calorimetry, rheometry, dynamic light scattering goniometry, and gel permeation chromatography. A 3-D percolation model is developed to simulate this monovinyl and divinyl copolymerization system. The simulation results agree well with the experimental observations qualitatively.