Fluorescence Method for Monitoring Gelation and Gel Swelling in Real Time

Abstract

Gelation by free-radical cross-linking copolymerization (FCC) of methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDM) was studied by real-time monitoring of pyrene (Py) intensity using the steady-state fluorescence (SSF) method. Samples with various cross-linker densities and toluene contents were prepared and gelations were observed at various temperatures. The percolation theory was employed to interpret the results. For all samples the gel fraction and the weight average degree of polymerization exponents s and γ were measured and found to be around 0.42 and 1.67, respectively. SSF measurements were then performed in order to study the swelling processes in gels prepared by FCC of MMA and EGDM at 75°C for various toluene contents. After drying the gels, swelling and desorption experiments were performed in toluene at 50 °C by real-time monitoring of Py fluorescence intensity. The Li-Tanaka equation was employed to produce the swelling parameters. Cooperative diffusion coefficients (Dc) were measured and found to be around 10-6 cm2/s for gels swollen in toluene.