Determination of pre-gelation and post-gelation activation energies during free radical crosslinking copolymerization

Steady-state fluorescence (SSF) and dilatoraetric techniques were used to study the freeradical crosslinking copolymerization (FCC) of styrene (S) and divinylbenzene (DVB) in bulk. The gel points (t_g) were recorded by dilatometry at various DVB contents and temperatures in pregelation regime during FCC process. Pyrene (Py) was used as a fluorescence probe for the in situ polymerization experiments. The time required for a sudden increase in the fluorescence intensity of Py was recorded for the samples at various DVB contents and temperatures. Py fluorescence intensity during FCC exhibits a sudden increase corresponding to the reaction time at which the rate of polymerization becomes maximum due to the gel effect in post-gelation regime. The onset of gel effect point (t_ge) was determined for various DVB contents and temperatures. The results show that alhough the dilatometric technique recorded the gel point, the fluorescence technique can be used to monitor the onset of the gel effect during S-DVB copolymerization. Pre-gelation and post-gelation actuation energies. ΔE_pre and ΔE _post were measured and it is observed that pre-gelation regime needs smaller energies than post-gelation regime during FCC.