Dissolution of Thin Poly(methyl methacrylate) Films in Ketones, Binary Ketone/Alcohol Mixtures, and Hydroxy Ketones

Abstract

Dissolution of poly(methyl methacrylate) thin films in ketones, alcohol/ketone mixtures, and hydroxy ketones was investigated using an in situ ellipsometer. The dissolution rate in pure ketones was limited by the penetration of solvent molecules into the polymer, as indicated by minimal swelling of the film during dissolution and significant solvent size effects. Activation energies for ketone dissolution were indicative of Case II penetration. Dissolution rate decreased with polymer molecular weight up to 105 g/mol, above which the rate was constant. The thickness of the swollen surface layer was estimated from shifts in the ellipsometric data. No surface layer was detected at a polymer molecular weight of, but above this value, the surface layer thickness increased with increasing molecular weight. The effects of polymer molecular weight on dissolution rate and thickness of the swollen layer indicated that at lower molecular weights, dissolution occurred by stress cracking. Case II transport model parameters were determined from the ketone dissolution data. Acetone/isopropanol mixtures at 20.4°C showed a transition from swelling to dissolution near 50% by volume acetone. Acetol, a hydroxy ketone, caused only swelling (34°–49°C), whereas diacetone alcohol dissolved the films (20.0°–36.9°C) at approximately one‐fourth the rate of methyl isobutyl ketone.