In situ fluorescence experiments to test the reliability of random bond and site bond percolation models during sol-gel transition in free-radical crosslinking copolymerization

Sol-gel phase transition during the free-radical crosslinking copolymerization of methyl methacrylate and ethylene glycol dimethacrylate was studied using the steady-state fluorescence method. Copolymerization was performed both in the absence and presence of toluene at 75°C. Sol-gel phase transitions were monitored by observing the direct intensity of an excited pyrene methyl pivalate during in situ fluorescence experiments. Random bond and site bond percolation models were employed to quantify the results of bulk and solution polymerizations, respectively, during the sol-gel phase transition. Gel points were determined and the β exponents were found to be around 0.37 and 0.38 during gelation in bulk and solution polymerizations, respectively.