Formation of rigid polyurethane foams with semi-fluorinated diblock copolymeric surfactants

Abstract

Semi-fluorinated diblock copolymers were employed as surfactants in the formation of water-blown closed cell rigid polyurethane foams by the ‘tube’-foam method. These fluorosurfactants consisted of a poly(methyl methacrylate) block and a poly[(1H,1H,2H,2H-perfluoroalkyl) methacrylate] block in which the perfluoroalkyl groups were either butyl or hexyl. As references, model foams were prepared with commercially applied siloxane surfactant, inert silica, and no surfactant. Foams based on the fluorosurfactants contained many small cells while the others showed larger and markedly more irregular cells. Scanning electron microscopy (SEM) and the average foam height (AFH) were used for characterization. SEM revealed that foam cell diameters as small as 100 μm could be realized when using fluorosurfactants in contrast to very large cell sizes and irregular shapes when a commercially available siloxane surfactant, an inert inorganic solid, or no surfactant at all were used. Furthermore, relatively large AFH-values were observed when only a semi-fluorinated diblock copolymer was used. However, the combination of siloxane surfactant with a fluorine-containing surfactant resulted in unparalleled high AFHs.