The low vapor pressure solvent 1-chloropentane was used to directly spin-cast polystyrene (PS) films onto poly(methyl methacrylate) (PMMA) with smooth surfaces and sharp interfaces. Interface roughness after removal of the PS layer with cyclohexane was determined with scanning force microscopy to be < 1 nn. Dynamic secondary mass spectroscopy revealed an interfacial width below the resolution limit of similar to 10 nm. Large area bilayers with smooth surfaces could be created. In addition, direct spincasting with 1-chloropentane allows the production of thin PS films (< 15 nm) and films of low molecular weight (< 5 kDa) PS, all of which would be impossible to produce for this important model system by the traditional water-transfer method. 1-chloropentane was confirmed to be a sufficiently selective solvent for PS by measuring the Flory-Huggins chi parameters of 1-chloropentane with PS and PMMA, respectively, with inverse gas chromatography. In the search for a suitable selective solvent, the authors have also examined the role of vapor pressure in spin casting smooth films over a wider molecular weight (4.3-190 kDa) and thickness range (similar to 5-500 nm) than previously reported. Only solvents with low vapor pressure produced high quality PS films. Methylcyclohexene can also be used to produce excellent, directly cast PS/PMMA bilayers, but with a smaller molecular weight and thickness window compared with 1-chloropentane. (c) 2006 Wiley Periodicals, Inc.