The fast transient fluorescence technique was used to study the sol-gel phase transition in free-radical crosslinking copolymerization of methyl methacrylate (MMA) and ethylene glycol dimethacrylate. Pyrene (Py) was used as a fluorescence probe for the in situ polymerization experiments. Fluorescence lifetimes of Py from its decay traces were measured and used to monitor the gelation process. Stern-Volmer kinetics was employed to determine the quenching rate constant before the onset of gelation. The MMA consumption rate was measured during the gelation process using the Stern-Volmer model. (C) 2000 Elsevier Science Ltd. Ail rights reserved.