In this study, a new approach for in situ monitoring of the monomer conversion based on the chemical interaction of a fluoroprobe, pyranine (8-hydroxypyrene-1,3,6-trisulfonic acid, trisodium salt), with polymer chains during the free radical crosslinking copolymerization of acrylamide/bisacrylamide system (AAm/Bis) has been developed. Recently, we have shown that the pyranine fluoroprobes added to the prepolymerization solution in trace amounts bind covalently to the vinyl groups of the growing polymer chains via OH group by radical addition when the free radical polymerization of acrylamide (AAm) is initiated. This covalent binding results in a considerable blue shift in the emission spectrum of the pyranine, from 515 to similar to 420 nm. In this study 0.5, 0.7, and 1.0 mol L-1 linear and crosslinked polymers including trace amounts of pyranine were synthesized. The change in the emission spectra of pyranine during polymerization and gelation were monitored as function of time. Here, we showed that both by theoretically and by comparing the fluorescence data with gravimetric measurements, the fluorescence intensity of pyranine monitored during the polymerization process can be used for in situ monitoring of the monomer conversion with great sensitivity. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 2455-2459, 2010