Methyl methacrylate was copolymerized with small amounts of ethylene glycol dimethacrylate. Monomer and pendant vinyl conversion as a function of time was measured up to the gel point. Pendant vinyl conversion was determined by 1H NMR. Plots of pendant conversion versus monomer conversion exhibit a positive y-intercept indicating the tendency to cyclize during the formation of a primary chain. For bulk systems, this amounted to approximately 3-4% of pendant vinyls and the cyclic proportion increased with dilution. The slope of the pendant versus monomer conversion plot is attributed to the formation of cross-links and subsequent cycles. A kinetic model is developed which includes constants for cyclization and pendant reactivity. Values for these constants for the chemical systems studied are evaluated. The average pendant vinyl reactivity is found to be approximately half that of monomeric vinyl reactivity.