The steady-state fluorescence technique was used to study the sol-gel transition in free radical crosslinking copolymerization of methyl methacrylate and ethylene glycol dimethacrylate (EGDM). Pyrene methyl pivalate was used as a fluorescence probe for the in situ polymerization experiments. The times required for the onset of gelation t(c) and the critical exponent beta were recorded for various EGDM contents and at different polymerization temperatures. A simple kinetic model was used to interpret the experimental gel point data. The results show that the fluorescence technique can be used to measure the critical exponent beta, the gel point t(c), and the activation energy during sol-gel phase transition processes. (C) 1996 John Wiley & Sons, Inc.