Fluorescence method to study gelation swelling and drying processes in gels formed by solution free radical copolymerization

Gelation during solution free radical crosslinking copolymerization (FCC) of methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDM) was studied by using the steady state fluorescence technique. FCC was performed in the presence of toluene at 75 °C. Sol-gel transitions were monitored by observing the direct intensity of an excited pyrene (P_y) during in situ fluorescence experiments for various toluene content. Gel points were determined and critical β exponents were found to be around 0.38. In situ swelling and drying experiments were performed at 50 °C by monitoring P_y intensity in disk-shaped gels produced by solution FCC. Li-Tanaka equation was employed to produce the cooperative diffusion coefficient, D_c for swelling process. D_c values were found to be around 10^-6 cm²/s at 50°C. It was also observed that loosly formed gels swell much faster than densely formed gels.