A Fluorescence Study on Dissolution Of Polymeric Glasses Prepared In Various Molecular Weights

By Önder Pekcan, Saziye Ugur

Poly(methyl methacrylate) (PMMA) discs in various molecular weights, Mw, were prepared by free-radical polymerization of methyl methacrylate (MMA). Pyrene (P) was introduced during polymerization as a fluorescence probe to monitor the gelation and dissolution processes in chloroform vapor and solvent, respectively. In-situ steady state fluorescence (SSF) experiments were performed to monitor vapor uptake and chain desorption processes.

Direct illumination of PMMA discs were performed to excite the P molecules embedded inside the PMMA glass. Variation in P intensity, I, was monitored during the swelling of the PMMA material exposed to chloroform vapor. It was observed that PMMA film swells like a crosslinked polymeric gel at early times by obeying the Li-Tanaka equation.

Swelling time constants, τc, of PMMA discs were measured and found to have a strong correlation with the molecular weight, of PMMA. In a separate experiment, when the PMMA discs were in chloroform, desorption of PMMA chains from glass discs was monitored by observing the change of pyrene fluorescence intensity.

A diffusion model with a moving boundary was employed to quantify the fluorescence data observed from dissolving PMMA discs made at various molecular weights. It was observed that desorption coefficient, D, decreased by increasing Mw by obeying the D≈Mw–1 law.