The bulk radical polymerization of three methacrylic monomers, butyl, dodecyl, and 3-[tris(trimethylsilyloxy)silyl] propyl methacrylate, were studied in the dark period after previous illumination by ultraviolet light at lambda = 365 nm. An important postpolymerization process took place in all the polymerization reactions. This indicates that, even at low monomer conversions, a certain and nonnegligible radical concentration remains after switching off radical production. Monomer concentration measurements by FT-IR spectroscopy in the dark period showed that long-lived radicals continued the polymerization up to conversions that, in some cases, were higher than 70%. The half-lifetimes of these macroradicals ranged from 300 to 14000 s. Kinetic expressions were developed to determine the fraction of living and dead polymer during the course of the postpolymerization. The SEC traces of the resulting polymers showed bimodal molecular weight distributions and extremely high-molecular-weight polymers obtained in the post-effect period. By means of both kinetic results and molecular weight distribution, the values of the radical concentration in the dark period, the average termination rate coefficient of the macroradicals, and the transfer constant to the monomer were determined for the different polymerizations reactions carried out.