Observation of critical opalescence in free radical crosslinking copolymerization of styrene and divinylbenzene by fluorescence method

In situ fluorescence technique was used to study the free-radical crosslink ing copolymerization of styrene and divinylbenzene in bulk. Pyrene (Py) was used as a fluorescence probe for the real time gelation experiments. The c ritical times, t(r) required for a dramatic increase in Py intensity, I-p, corresponding to the onset of the gel effect were determined. The spikes in I,curves were also observed at high crosslinker densities. These spikes we re attributed to the existence of "critical opalescence" during the gel for mation process where two different gel phases having two different concentr ations coexist. to values at which the critical opalescence is occurred are recorded in the close vicinity of the t(r) points. (C) 1999 Elsevier Scien ce Ltd. All rights reserved.