Studying the sol–gel transition of styrene–divinyl benzene crosslinking co-polymerization via excimer forming dye molecules

A novel method based on the steady state fluorescence technique was used to study the sol–gel transition in the free radical crosslinking reaction between styrene (St) and divinyl benzene (DVB) with 2,2′-azobisisobutyronitrile (AIBN) as initiator. N-(4-(pyrenyl methylene)-oxycarbonyl phenyl)maleimide (Py-MI) was used as a fluorescence probe. The possible enchainment of Py-MI in alternating sequences occurred randomly in polymer clusters produced modifications in the fluorescence spectra, namely the shift at the higher wavelengths due to the excimer formation. The fluorescence spectra of Py-MIʹs excimers allowed both to monitor the sol–gel transition and to test the critical exponents as function of co-monomerʹs concentration. The gel fraction exponent β and the weight average degree of polymerization exponent γ agreed best with the static percolation values. Although this technique was applied for St–DVB co-polymerization, it may be generalized for the other monomers that are able to bind chemically to Py-MI monomer during the polymerization.