Microcellular Materials via Polymerization in Supercritical Fluids

A process is demonstrated whereby microcellular polymer foams can be obtained by polymerization directly in a near-critical diluent. Critical point drying can then be effected in the reactor vessel in a relatively efficient manner. The key to the process is the choice of diluent and matching it to the polymer system to be gelled and dried. Propane and Freon-22 were studied as diluents with the polymer system of poly(methyl methacrylate-co-ethylene glycol-dimethacrylate). Freon-22 proved to be the superior choice. Morphology and density of the resulting materials were comparable to microcellular foams prepared by a more conventional carbon dioxide wash and dry approach.