Fast transient fluorescence (FTRF) technique was used to study the sol-gel phase transition in free-radical crosslinking copolymerization of methyl methacrylate (MMA), ethyl methacrylate (EMA) and their mixtures with ethylene glycol dimethacryalate (EGDM). Fluorescence lifetimes of pyrene (Py) front its decay traces were monitored during sol-gel phase transitions. Consumption of MMA and/or EMA in pregel solutions due to gel formation dramatically increased the Py fluorescence lifetimes, in which were used to study the gelation of M MA EMA and their mixtures as a function of time, at various temperatures and monomer concentrations. Monomer consumption rates, k(r) were measured during sol-gel transition process by using Stern-Volmer model. Gelation activation energies DeltaE(G) were determined and found to be 14 and 10 kcal mol(-1) for MMA and EMA respectively. (C) 2004 Elsevier B.V. All rights reserved.